usually a pyro for multiple reasons
1) I fucking hate spies more than anything, if there was ever a sole purpose for me in gaming it is to destroy all spies.
2) I love droppin in on a group of 2-3 baddies and lighting the whole room ablaze then watch them squirrelishly run trying to get health, so satisfying.
3) I always use the detonator to annoy the piss out of snipers/long range weapon users, due to the alt fire explosion ability, even with them hiding behind cover, I get you
also, nothing greater than blowing up a demo/soldier than firing back at them their own ammo, i still remember getting a triple kill midair while eturning with a crit rocket fired at me, so glorious, my teammate medic took the intel ftw shortly afterwards.