I like playing a caster, but I hate the state of Moonkin DPS. It feels even more half-assed than it did in Cataclysm. The multi-dotting is anemic, the dedicated AoE abilities are useless, burst is pathetic, and the sustained damage output is extremely poor in every situation outside of Patchwerk-type DPS burns. So I used JP and guild perks to get all of the cloth heirlooms some time ago, and since then I've leveled all three of the cloth classes up to around level 50 to figure out which kind of playstyle I like.
Mage: I like the Arcane playstyle, and at low level mana management is as simple as blowing Arcane Barrage when you get low. At endgame, it seems like it is a nightmare with the way you have basically stay over 80% all the time. Frost is fine solo, but doesn't work well in dungeons where the tank's AoE attacks remove your freezes as fast as you apply them, and Fingers of Frost procs are painfully infrequent. Still does equal or more damage than Arcane.
Warlock: Destruction has positively silly burst and one of the easiest rotations I've played. It just blows shit up effortlessly. Affliction has no burst and the hardest rotation I've played, definitely one of the late bloomer specs.. one of our guildies is playing it at 90 and the sustained DPS output is far better than Destruction.
Priest: Call me crazy, but I actually like the mechanic of consuming DoTs with Shadow Word: Insanity. It's a nice way of backloading burst DPS, similar to Affliction in a few ways; however, the instant damage component on SW

ain means the AoE performance in instances is better. However, this is the only spec out of the ones I played where I was running out of mana during sustained encounters. I don't know if this is a typical experience.
I also tried Disc healing, which I've found to be more than adequate in any situation, but it's also a little off-putting with the delay between the when nuke hits and the Atonement heal lands. It also seems very reliant on damage absorbs, which means if I don't know what's coming, I feel caught with my pants down. It doesn't have the ability to recover quickly from an adverse situation the way a Druid does.