I enjoy sniper(huntsman/jarate set) on offense or defense, but pyro is a lot of fun provided it's not a payload match. If I can get away with it I love to play Scout on defense- coming up on an enemy's flank and blasting them to bits with a point-blank Force-A-Nature is probably the most satisfying part of the game.
I bet a few nice jokes will come from this, but still..I have the feeling that I've only read half of this week's comic. Sure, this is a nice plottwist, but that doesn't mean that I don't want a joke at the end of every comic anymore.
Depends on the map, situation and what I'm feeling like. So for example, if we've been pushed back to the second cap, I'll spy behind them and backstab people as they make their way to the front. For general purpose though, I'll normally play medic or heavy.