Hey! I'd vote for Spykecam! (lol, j/k, thought that was truely a horrible episode as well).
This is a hard question, but I'm going to have to say it is a 3-way tie between:
Speed and Spyke: Introduced one of my fave. characters on the show (Pietro) and it was actually the first episode I ever saw.
Survival of the Fittest: This episode was just fun. The Brotherhood and the X-men in a bootcamp of sorts, got a lot of laughs out of this one.
Shadowed Past: Poor Kurt, I thought this episode was really done well.