Sniper is too easy, unless you use the Huntsman. Then it's fun and challenging.

It depends on the map for my class choice.
Open areas are my scout, sniper, or spy choices.
Tight, but short hallways are my engineer choices.
Your basic Valve maps with different environments.. I usually just choose whatever I feel like playing, which can be any class.
My rage class is pyro, since it's so damn powerful.
Now, I'm gonna go lie back down.. I'm getting dizzy again.