I guess I'd be an engineer if it were capture the flag or point because it's the only character I can play that contributes to my team in some way. Also, I'm not one for extreme action, so I like the more laid-back strategy of the engineer.
It's also a lot of fun to play with fellow engineers, as you have your own little team within your team.
If it's deathmatch-style, I'd probably go with scout, just because he is fun. But, I know I'll die within a short period of time.
When pushing carts, I like the soldier for his weaponry.
Favorite: engineer.