In order from most favorite to least;
Sniper: I am just awesome with Snipers, if I do say so myself. Nothing like getting 4 headshots in a row due to noobie Snipers/Engies.
Spy: I'm not too good with the spy, but when I'm on a role, I'm on a role. Usually in quick backstabbing bursts.
Scout: I do enjoy running around with this class at times.
Medic: I only play as him when there is a severe lack of them on the map, but I do enjoy being in the support role every so often.
Demoman: Not particularly good at them, but occasionally I like going Demoknight for my own amusement.
Soldier: Just a bit too boring for me. I always feel like I would prefer an assault rifle instead of a rocket launcher for him, though that would be odd in TF2.
Heavy: His play style is a bit too simple for me, but every now and again he's fun to play as. Got, like, 28 points in one life when I stood on top of the payload cart, nearly got the final terminus. It was glorious.
Pyros: Never was too good with them. The whole "W+M1" strategy does not work for me as I am always just out of range for my flamethrower and no matter what I do, even if I light them up for 4 seconds, they still somehow survive.
Engineers: Again, I only really play them when we need a teleporter, but I just cannot seem to land any kills with my sentries. Bit too much of a defensive and boring class for me.