My favorite class in any version of D&D is probably the 2nd edition AD&D bard. You can wield a sword (or any other weapon), but you kinda suck at it. You can play around with arcane spells, but you are clearly inferior to an actual wizard. You can attempt several thieving abilities, but you're not as good as a real deal thief. You can wear armor up to chainmail and play the mandolin or flute or something and maybe inspire the troops a little bit. In short, you have a wide variety of interesting things you can try to do, just don't expect to be very good at any of them. You have a good reason to try to talk to a lot of monsters, but also several neat little tricks when that fails.
In fact I once got into a rather ridiculously intense email argument with a DM over the second edition Bard. He was gearing up to run a 2nd ed. campaign and looking for players. I suggested that I would like to test my theory that a half-elf bard makes a better Gandalf than the standard Mage type classes. Wield a sword? Check. Give inspiring speeches on the eve of battle? Check. Know things about mysterious magic rings? Check. Use persuasion to forge new alliances? Check. Cast spells only after other avenues are exhausted? Checkity-check. And the half-elf part gave me a slightly elonged lifespan over mere men while still allowing me to move amongst them as if one of their own.
Despite being a veteran HERO System player who understood the difference between fluff and crunch, he absolutely rejected my character concept out of hand. Never mind that my choice of class and race was perfectly legit under the rules, dude just didn't think it made any sense to play a wizard using any other class than the normal one prescribed. If I was to play a bard, he would expect me to carry a lute and dress in poofy-sleeved vests and whatnot. My head nearly exploded with frustration.
Anyway, that's water long under the bridge. What's your favorite class and why?