It's hard to say. If you're talking about "official" D&D, I really don't want to play 4e again. For 3.5e, I'd like to play a bard again, straight up, likewise for Pathfinder (though I've never played a bard in Pathfinder).
Yet right now I just want to play old school D&D, 2e or earlier, or a retroclone. I'd be happy playing a fighter or thief, or even a bard in those systems. Right now I'm really keen on DCC RPG. I'm running it, but would love to play any of the classes in that game. Such is often the life of a game master--nearly always running games but hardly ever getting to actually play.