I've tended to avoid playing Paladin, Barbarian, Bard, and to some extent Druid. I view that these classes (with the near exception of druid) are specialized versions of combinations of the various other core classes. Almost to the point of being stereotypes.
Paladin: I find the alignment to constraining on me and the party, and the potential to get stripped of your powers by DM fiat/misunderstanding is annoying. Having to contstantly distract the paladin when the group wants to do a neutral, chaotic act is annoying. Plus, the holier-than-thou attitude can get old. Why not play a fighter/priest of a lawful good god = less baggage.
Barbarian: This is just a variant on fighter. The speedy, angry, dumb fighter. Not that its a bad class to play mechanistically wise. It just seems to be a narrowly defined stereotype. Though, I have played them.
Bard: The singing, instrument playing charismatic subvariant of the wizard. I really think the problem with this class is that they wanted a jack-of-all-trades but they couldn't give up on the bard music idea, so they crammed them into one class. It just doesn't work. I'd have rather seen that the bard was a prestige class for wizards. Then make a new class called say The Generalist that was semi good at everything: mid fighter, mid arcase caster, mid skills etc...
Druid: While I love the class and the idea, I'm even playing one right now, the fact that your spell list is suboptimal in dungeon and city encounters gets old real quick. Couldn't they have designed some new spells for the druid to make them more effective outside of the woods? I keep wishing that I had played a cleric of nature, especially since there aren't any clerics in the party.