I love Warlock's flavor and they're super fun to play with. Killing your own guys, hurting yourself and then BAM! you surprise your opponent (who up to this point, thought you were crazy) with a nice combo. They're just not a consistent class is all.
I also like Priest for this reason - I can get a 6/6 with the ability to draw a card for every dmg it takes on turn 3 if I go second.
For pure, consistent power, I would pick hunter.
I have to pick one, and that was Warlock though.