Shocked Monk and Psion aren't getting more (undeserved) hate, based on the kinds of topics you tend to see on the forums...
So anyway, I voted Fighter. Often the most beloved class on these forums. Over the years, as I've tried to balance the other non-casters, I've steadily grown to hate this generic, completely flavor-devoid class. There isn't a martial-caster disparity often, the problem is framed ONLY in the terms of "fighter is underpowered!" But that's just the tip of my hate-berg. Anything I try to do to buff classes other than Fighter (who I also try to buff, it just tends to attract less flak when I buff him) there's this glass ceiling. "You can't out fight the fighter!" It doesn't matter what style of fighting it is, whether it's skirmishing, archery...whatever. Because "a fighter's job is fighting! It's in his name! He must be the best at it!" it ends up being a cement block around the feet of other underpriviledged characters in the ocean of D&D. Anything to buff the fighter has to maintain his generic "capable of anything" crap else it loses the "flavor" of being a Fighter.
I'm sick of it. Please, just go away, you horrible boring class that's about nothing more than how many +'s you have on rolls. I hate you. Give me a bunch of different martial classes to cover different things that are actually hyper capable of those things. Give me swashbuckling duelists who can parry spells. 2H weapon wielders that can heft giant swords and create avalanches by cleaving into the side of a mountain. Give me archers who can blot out the sun with arrows and shoot just fine in melee, disarming you of your sword as you're charging at him and in midswing.
Just not the generic fighter. Please.