I generally play Engie, Soldier, Demo, or Spy and do pretty well with all of them. I'm still ranked in the low 50s out of 6,000+ on the 360 Ranked Leaderboard. The only class I still really suck at is Pyro. Other than being one of the best ways to shut down Spies, I can't seem to get any use out of them.
I like Heavy too, but they're always going to be fodder for pretty much any capable class. They're an important target and Spies are just something you sort of have to deal with or switch classes to combat the problem.
I'm pretty good at sniping on 360; I've got a knack for it in other games. Even so, the class is a waste on most maps if you aren't consistent or if you're positioning yourself wrong. The maximum player count on 360 is too low to have someone idling with their sniper rifle and contributing nothing.
What time are you on, Willco? Let me know if you wanna get a game going.