If I was asked to do the fighters' passes and had insight into what they'd be up to Steve beforehand here's who I'd choose:
Bonus:
Muddy Mole
FP1:
Crash Bandicoot
Banjo-Kazooie
Hero
Terry
Doomguy
FP2:
Waluigi
Steve
PaRappa the Rapper
Dr. Eggman/Tails/Knuckles (3 characters and stages for the price of 1, if you think that's cheating choose whichever one you like best)
CJ (GTA)
Space Invader
Bonus:
Muddy Mole
FP1:
Crash Bandicoot
Banjo-Kazooie
Hero
Terry
Doomguy
FP2:
Waluigi
Steve
PaRappa the Rapper
Dr. Eggman/Tails/Knuckles (3 characters and stages for the price of 1, if you think that's cheating choose whichever one you like best)
CJ (GTA)
Space Invader