Each role has its ups and downs. Some I like better in circumstances more than others. Having played all three (four of you count melee and ranged as two different ones, which I do) I can make a personal judgement on them based on situations. We all have our personal opinions, these are mine.
Low Level Dungeons:
Tank: I dislike being a tank in low level dungeons because there more than any place else you really need to know the dungeons. They are not like BC, Wrath and Cata where everything is easily set forward. I still get lost in some dungeons and that is why I do not like tanking them. It usually ends up one of two ways. Way one, you need to lead and know where to go or way two happens. Way two, some idiot DPS or healer will run ahead of you and pull everything for you and then complain if they die because you did not get aggro off of them.
Also, low level dungeons seem to have more "we are invincible" attitude than high level ones from many of the players. Low level dungeons are more often to turn into a wipe at a moments notice for no good reason because of people that do not understand that tanks do not have as many aggro generating tools and healers do not have as many heals and most definitely not quick heals and AoE heals at lowest levels. Any failures here always fall on the tanks back when in truth 80% of the time wipes in low level dungeons have more to do with the DPS then the tanks or healers.
Healer: This is hit or miss really and it usually depends on the tank more then anything else. If you have a tank that notices that most heals are something along the lines of 3 second casts and that mana is a very limited resource then healing low level dungeons can be really easy and fun. If you get a tank that never lets you drink and keeps pulling or pulls too much, incoming wipefest, and there is nothing you can do about it with your long cast heals and even more limited toolbox.
One good part about it is that as a healer, if you speak up and do not act like a jerk 99 out of 100 times the group will side with you. One line like, I am sorry but there where too many mobs and I only have so much mana at this level. Or, could you please let me drink next time before pulling the boss, I burn through mana so quick at this level. Either of those politely said lines and the 3 DPS, unless they are grouped with the tank to begin with, will always be on your side.
Melee DPS: Low level dungeons can really be fun for melee. Things die so quick but you have no cast time moves which means you get maximum up time. Also, if the tank goes down and you have a remotely competent healer combined with knowing how to play your class and using whatever ability you have to adapt to being the tank now you can tank nearly anything at low levels as a melee, yes, even as a rogue.
Ranged DPS: This is both good and bad. Ranged usually get some decent AoE early on and in low level dungeons you can live with AoE only for the most part. The bad is that everything dies so fast, which means if you try to actually do anything even remotely resembling a rotation you will do nothing. It will go like this. Pick a target, start casting, just as cast is about to finish, mob dies, cast interrupted. Tab to next mob, start casting, just as the cast is about to finish, mob dies, cast interrupted. It is completely annoying and frustrating to the 10th degree.
Even worse if you are a hunter. Casters can do instants and drink when they need mana. When hunters need focus, they need to steady to get it back. Most mobs die within the cast time of a hunters steady. This means auto shoot only most of the time but if you are an experienced hunter, you can easily compensate, but like all casters in low level dungeons, it is just no fun.
Learning The Role:
Tank: Learning to tank can be a very daunting task. You can only really do it in a group setting which means unless you assemble the group yourself any failures are for everyone else to see and ridicule you about. This could very well be the reason there are not many tanks. Unless you pick up really quickly on things and can move from reading to implementing smoothly and quick, you will fail and you will need think skin to deal with all the fail tank remarks.
One good thing is that if you are somewhat lacking most of the times a melee can handle a few hits before you taunt back. In many cases the healer can compensate while you are learning the best times to use cooldowns. You can make some failures along the way and not have any ill effects from it because there are others there to compensate for you.
While learning to tank can be amazingly difficult in ways that non tanks will never be fully capable of understanding it is in the same richly rewarding once you do it right because you get to feel like the superhero of the group once you got it down.
Healer: Tanking is hard but can be learned with people around you being bad. Healing is impossible to learn with people around you being bad. Tank pulls to much you try to cast your long big heal, tank dies. Tank pulls to much next time, you try to cast an instant, an HoT, and anything else fast you have, tank dies. Tank pulls to much a third time and you try to cast something instant, something fast and expensive and then roll out the long big heal, tank dies. See, you just went through the entire learning process and tied a few different ways to deal with the situation but the tank died every time.
It is not your fault, it is the tanks. Does he have a stun he can use, an interrupt for the caster he can use, CC he could have asked for, the ability to pull less? If any of those are true, and I am sure at least one is, the tank is a bad tank and you can never see that learning process you just went through actually work because at the moment you are incapable of doing it. It is not possible with your gear and abilities while learning.
If you have DPS that are pulling aggro and running away from the tank. If you have DPS that are all attacking different mobs. If you have a group that does not notice you are being attacked and no one helps. If you have bad players, it is nearly impossible to learn. Side note, yes, bad groups later on teach you to become a better healer, this part is about learning, learning with bad groups makes you pull your hair out. It makes you quit. This could be part of the reason we have a healer shortage just like we have a tank shortage. Learning at the start is really hard sometimes.
DPS Melee & Ranged: Without doubt it is the easiest role to learn. You attack what the tank is attacking and has the most aggro on. Even if you are someone that rides the short yellow bus you will get the idea that if you attack things the tank is not attacking or the tank does not have aggro on you will die. That is your learning process. Hit buttons, do damage, don't do something that gets you killed.
Perfecting Your Craft:
Tank: Once you know your role perfecting it as a tank is probably one of the easiest things. Once you know how to pull mobs, all mobs are the same. Doesn't make a difference if it is 2 casters and 3 melee at level 35 or 85, you will pull them the same, just with more useful abilities at higher levels. Also, at higher levels when you get new abilities they are easier for you to identify as a tank then as a healer or DPS. This basically means, once you know how to tank, you know how to tank. You will just get better at doing things cleaner. You will get better with interrupts, with stuns, with cooldown usage, with integrating DPS into your tanking. Once you know the role you know the role. Once you can do it, you can do it. Bare minimum is can do. You can do the job with bare minimum. So you have time to perfect your craft.
Healer: Healer is like the tank in one way. Once you can do it, you can do it. If bare minimum is keeping people alive and you can do that you can get by with bare minimum. From that point on it is just a matter of doing it more efficiently and making it less stressful for yourself. Unlike tanks where new abilities are usually a clear cut what is better healers do not have that luxury. Some abilities might seem like a good thing but really are not. Some things just don't scream out at you how to use them like they do with a tank. Perfecting your craft as a healer is much more involved then it is for a tank.
Melee & Ranged DPS: As easy as it is to DPS to start with is as hard as it is to master it later on. Like healers they do not have the luxury of an upgrade to an ability being as clear cut as possible. Where a tank and a healer don't use a rotation, they react, a damage dealer needs to use a rotation, or priority if you will. There is a perfect way to do things and that will always offer the best results. There is a perfect way to do your rotation, or priority. There is a perfect way to time your abilities being it spamming or waiting a half a second. There is a perfect way of using cooldowns. There is perfection and there is you. You will never meet perfection, ever, even if you play for a million years. That is why mastering the craft of DPS is the hardest part of the game.
Simplest way to explain the perfecting your craft differences it to join up in a pug on your local server. If you tank or heal and say you have done the fight before, 95% of the time it is an instant invite, no further question asked. Like I said, if you can do it, you can do it when it comes to tanking and healing. For a DPS they will ask what your DPS is and if they do not feel it is up to what they want you do not get an invite. Saying, I've done it as a damage dealer is just not acceptable. Damage dealers can not just get away with having to have done it, they need to have done it well.
Tank: Leveling as a tank in today's world is a beautiful thing. Walk into a zone and start pulling, round up half the zone, 20 minutes later take a breath and get read to spend the next 5 minutes looting. There has never been a better case for AoE looting then tank questing. Even more so if you are questing as a warrior or a bear. The more mobs the better for them. One on one killing can take time but twenty on one killing takes almost the same amount of time as one on one would. Some can argue that tank questing might be in a position right now where it is the best way to level, at least if you are a melee class that has the option of a tank spec.
Healer: Healer questing means you hate your life and you want to make things as hard as humanly possible. With the exception of discipline priest questing, which is quite effective, healers are not exactly built to quest. Can they do it? Yes. Should they do it? Not unless you are Disc.
Melee DPS: If you are a DK, warrior or paladin spec for tanking or you are bound to die a little more often then you might like. If you are a cat, make good use of bear if you want to survive. If you are a rogue, too bad so sad. Recuperation makes life bearable as a rogue in today's world, but no one wearing leather should be getting beat on and more so beat on my multiple mobs. Melee questing can be very effective. One on one and you will speed through it no problem what so ever but once you get a few mobs you might be in trouble. Good thing for melee that all those elite quests where changed in outlands and wrath because unless you where extremely good at your class there was no way a non tank could get that close to one of those melee mobs and not die.
Ranged DPS: Always has been and always will be the best leveling role in the game. Keep things at a distance and hopefully kill it before it gets to you. All ranged classes can be OP when it comes to questing but none more so then hunters with the personal tank. Ranged got it easy when it comes to questing and hunters got it easy when it comes to being ranged. Being the game has changed so much however the hunter advantage of having the personal tank is evaporating. Any ranged class can burn down any mob in mere seconds making the need for the personal tank a great deal less.
Tank: It depends on the content you are soloing but all tanks can easily solo a vast majority of dated content out there. At least all old dungeons. Only blood DKs however can go all psycho with their soloing content. paladins might be able to get some extreme soloing done but warriors and druids are a no go. If you want to solo content as a tank, do it as a blood DK.
Healer: You're kidding me right? They might be able to solo some classic dungeons at 85. Disc can even solo some classic raid content. I don't think any healer spec can even get past BC normals and if they do the skill involved most likely means the people capable of doing it are few and far between.
Melee DPS: They can solo a fair deal of content but not nearly as much as their tanking counter parts in most cases. Some melee classes can pull off some really interesting soloing but the skill level and preparations required means that not many could do it leaving melee and soloing just a step above healers. This means they can do some but it is not exactly practical.
Ranged DPS: If you read a lot on the forums you will see some new ranged DPS soloing something insane nearly every week. Just like they are the best questers they are also the best soloers. While blood DKs get all the press ranged classes have been doing it for a long and and it is a lot easier to do it with them. While the skill level required for a blood DK to solo some of the content they have soloed is insane, the skill cap for many fights, not all, for a ranged to solo some harder content is not anywhere in the same ballpark. I am an average hunter and was soloing 85 heroics a few months into the expansion. Good ones have soloed nearly all the original ones. There have been mages, warlocks, hunters and shadow priests soloing insane stuff all expansion. While there are many things they can not solo when you look at the average player and what the average player can do, if you want to solo you can solo as ranged a lot easier then you could solo stuff blood DKs are doing. No other role can come close to it.
Tanks: Crafting and crafting only here. Jewelcrafting is ideal here but not talking about bonuses here. I am talking about practicality. Your dungeon queue will always be instant. If you have a healing off spec your raid queue will be instant too. If you have a DPS offspec it will be a small wait and in that time you can make some crafts to sell on the market. If you are tank only, like I usually am, perhaps a gathering profession might be in order. Usually mining if anything for me. At least you can mine some while waiting in the raid queue.
Healer: You will never wait for the raid queue. You will never wait long for the dungeon queue. This means crafting and crafting only. A gathering profession on a healer is a waste. You will never have the free time doing nothing to actively go gathering.
Melee & Ranged DPS: Unless you have a tank or healer offspec to work with to speed up queue times you are going to spend your life waiting. Might as well put that time to good use. Get a gathering profession. Unless you are in a hard mode server first type guild where you need to maximize your profession bonus it is really no big deal to have a gathering profession. While waiting in queue for the raid finder and dungeon finder, which you will have to wait for, you can be out and about gathering. At least you are making money doing something while waiting instead of sitting in some city letting your brain rot reading trade chat.
Tank: I find raid leading as a tank much easier then in any other role. I have my task and that is what I am focused on and like I said earlier about tanking once you know how to do it you know how to do it. This gives me more available time to keep track of life totals, timers, when the big moves are going to come, etc. Not to mention, I am facing the raid when tanking and usually there is nothing behind me. Sure, I have this big thing in front of me but it is not as bad as having your back to all the action. Being many of the annoying mechanics never target the tank, this also means I am in the position that is the least likely to require moment which once again allows me to control everything that is going around and announcing any strategic changes on the fly.
Healer: I hate raid leading as the healer. While I am in a much better position to see what others are doing and unlike the tank I can see the entire raid easily instead of just some mobs crotch and whatever is visible around it. Then again I tend to take healing a great deal more serious which usually means I get more focused and can sometimes miss things I should be calling out. With an experienced group that does not need anything called out, this is fine, but while learning a fight or teaching it to new people, this could serve as a problem.
Melee DPS: I don't know why, I just can't raid lead as melee DPS. Maybe it is all the spell effects. Maybe it is me not being extremely good at any melee class to the point where I do not need to even think about my rotation. Maybe it is the stink coming from the bosses butt that distracts me. Maybe it is having my back to the raid. It could be a million things but I just do not feel like raid leading as a melee DPS gives me a good position to do it.
Ranged DPS: Next to tanking this is the best position to raid lead from for me. You can see everything that is going on, more so then the tank even. While it does give a little added difficultly because you need to keep optimum rotation for maximum DPS, move as needed and call out everything, it is a lot easier then doing it from a healers standpoint which is the same basically. If I make a mistake in my rotation I might drop 1K DPS which in most cases will not cause a wipe as opposed to if I make a mistake in healing it could drop one player, which could in most cases cause a wipe depending on who that person is.
Tank: When you want it nice and easy this is the way to go. Just like a healer always trying to be better and a damage dealer always trying to do more damage you will always be trying to do more damage, to better time your cooldowns, etc. The one main difference is, if you group can do the fight at your current skill level, it is not required. You can sit back and relax and get the easiest job on the way to loot. I always like to improve but it is nice to do something once in a while where you don't feel like you have to because there is no pressure on you.
Healing: I love healing when the fight is new. I love learning a new fight and healing on the fly before I know all the patterns for when damage is coming and where it is coming from and who it is going to. I know my tools on how to heal so it is basically just doing what I know how to do in a different way. Sadly a great deal of fights are only exciting that first time or two. Once you got it down and everyone you are with got it down it gets boring fast really.
Melee & Ranged DPS: This is where the action is when it comes to raiding. Once the tank is tanking it fine and once the healers are healing it fine they can just chill out and collect loot. However, as a damage dealer that is what you are all about. If you did 28K today you want to do 28500 next week and 29000 the week after. While it is not required, you could use the same argument about DPS as you do about tanking and healing and say once you can do it you can do it, it is not the same. 13K was faceroll if everyone was doing that in ICC back when it was out but you do not see people doing that now. Nope, they are pushing it to see how high they can get. Tanks and heals can rest as soon as they can get it done. DPS can never rest. There is always room to get better and always new heights to reach when it comes to doing damage. DPS is where it is at, it is where good enough is never good enough.
Tank: The large majority of the fights for tanks are pick a spot, tank the mobs there, and use cooldowns at a set time that never deviates. Hence the reason I say tanking is the easiest job in the game when it comes to raiding. I find fights like that boring as sin. I love add fights. I love having to run around and gather things up. I love having to move the boss in a manner that keep it in range of the ranged as well as move it at a pace that melee can keep DPSing it. I love active tanking fights. There are not enough of them if you ask me. If I am going to have just stand there I would prefer DPS tank fights where I DPS more then I tank. It makes it more fun for me. Nothing fun about standing in one place popping cooldowns at 30, 60 or 90 second intervals and never moving so might as well think of them as DPSing tank fights to spice it up.
Healers: I love the newness of fights like I mentioned before. I love the feeling of the sense of urgency. I love feeling like anyone can die at any given moment. I love healing like a mad man hoping, praying that my mana does not run out before the boss dies. I love the pressure, it invigorates me. I dislike just healing the tank and having to deal with huge damage spikes. Healing like that always seems to feel luck based more then skill based. I dislike having raid damage that is instantly deadly. I like it when I have a chance to respond and it is cast, cast, cast non stop. This is how healing should always be. Everyone getting damage all the time, you going crazy keeping people up, it is a race to the enrage timer and the enrage timer is you mana bar. Now that is exciting.
Melee DPS: I love stand still fights where I can just practice my rotation like on a target dummy. I hate movement fights and target switching fights where I need to run all over the place. It always feels like I am starting all over from the beginning when I have to do that. I am not saying I just want to stay on the boss and pad my DPS numbers when I melee. I have no problems with needing to interrupt, disarm, etc. I do not mind if there are tasks that require me to do things other than damage but I hate running all over the place. The run distance between where I am and where I need to be always feels like wasted time where I am doing nothing and it makes me feel basically useless. If you noticed my comment about DPS having gathering professions so they can put their time waiting in queue to good use you will see it is not just a DPS thing. Wasted time doing nothing is wasted time. I don't like wasted time which means I don't like running all over the place to get to mobs.
Ranged DPS: I don't have the same problem I do with melee. Target switching, no problem. Boss moving, no problem. I enjoy most fights as ranged. The only thing I really hate as ranged is when we are forced to move every two seconds. Cast, move, cast, move, cast, move, that crap is for PvP, not raiding. Otherwise, ranged is fun, no matter the mechanics.
I think I babbled enough for today.
Do you see things differently depending on which roll you play like I do?