Pyro. And, of course, because I'm a cheap bastard, I use the Backburner/Axetinguisher combo =D
If not that, then a Soldier with my Vintage Direct Hit, or a Scout with my Force 'O Nature.
Edit: Oh, this is FPS' in general. I play Support, Scout or Stealth. For example, I play a Support Spec. in Killing Floor, I'm a dedicated shotgunner/medic in L4D2, and I play engi, using a shotgun with 12 Gauge slugs in BFBC2. In Medal Of Honour, I played sniper, in CoD (When I played that pile of shit) I was always a submachine gunner.
Yeah, I'm either the guy keeping you alive, the guy running in and wiping things out, or the guy staying behind the sidelines, silently killing as he goes. And I enjoy all three equally.
[sub][sub]There's an art to being a good Pyro...[/sub][/sub]