Warlock.
Back in Late Wrath, Warlocks were OK.
They played a lot like a hunter that casted spells, though the whole "hurt yourself to replenish your mana, then steal HP from mobs" got a little old after constantly doing nothing but that and the occasional DoT/Incinerate, but it is much, so very much better than what we have Now.
Now, Demo (the only warlock spec I ever really tried) is "Immolate, HoG and pray you don't crit with it, and Incinerate, pray it dies before it gets more than 1-2 hits on you".
Your pet can no longer tank (you rip threat off it after the first Incinerate, if your HoG didn't crit... if your HoG crit, that mob is *glued* on you) because they felt the need to remove the Felguard's Taunt (I suppose because some warlocks were too stupid to turn it off in groups).
The only pet that DOES have a "taunt", is the blueberry.
It has no charge (making it useless as a tank pet) and the "taunt" builds next to zero threat whatsoever. You seriously have to let the thing melee and taunt for nearly 10 seconds before you can actually start casting and NOT pull threat off your pet.
My Warlock is still sitting at Level 80 -- someday, I might do the cooking/fishing dailies to get him to 85, but I doubt I'll do much, if any, questing with him whatsoever until/unless they fix solo Warlock.
Other than Warlocks...
I'd have to say I enjoy the other 9 classes, Paladins are good if you're Prot, I feel that Prot Warriors are also pretty good (though I wish they gave them some healing that didn't involve landing killing blows/taking a mob to 20% or lower), Druids are fairly fun to play, though I tend to use Cat instead of Bear. Shamans are cool, Enhance doesn't even NEED totems (I usually only throw them in Tol Barad when I get 2 mobs on me or if I need to fight an elite), Arcane Mage is kinda fun, Combat Rogue ain't too bad either, and BM Hunters are easy-peasy, while Blood DKs are still as cool as ever.
So yeah... Warlock is the one and only class I dislike.