Favorite(s):
Demoman- great for defense, which is what i like, but also an amazing guy to have to take out that bunker of snipers who is being annoying as hell with piss rifles or whatever
Heavy- it's just alot of fun, big pile of meat with a minigun? can't get too much better.
LEAST favorite(s):
Spy- I fucking hate these with a passion, and i'm pretty sure i'm a magnet to them but anytime there is a room with at least 2 spies on the other team i dedicate my full attention/time to pyro'ing the entire room until hell seems cozier than that server, and once the spies are gone i immediately pyro off.
Engineer- A great engineer(or set of engineers) can make or break some servers, literally, if they get the right angles to setup and have the other teammates supporting them, they are near unstoppable at some points (depending on the map also)
edit: The fucking soldier with the right combo (including the black box, fucking douche gun) can be annoying as hell to kill, fucking terminator tank rolling at you with splash damage healing, regardless of having a small clip, is a pain in the butt to deal with, which if i do notice annoying people with these combos i definitely roll out with the pyro and troll the shit out of their rockets and destroy em that way