spy, battle medic, battle engi, & pyro. On battle medic that means Im always on the front lines not only healing but also fighting. When my friend is on we ubersaw their spawn. battle engi is usually running the mini sentries but I run the regular sentries & upgrade to the max level then goto the front lines. on pyro I use the degreaser & just send projectiles back & the basic shotgun or the flare gun. I might use the sniper with the huntsmen if I feel like acting like a dick.
But I prefer running spy since I can keep the other team reinforcements by running kuni, dead ringer & the basic revolver. Just lining up dem chain backstabs.