First team? Yusuke Urameshi, Hiei, and Kurama from Yu Yu Hakusho. There are games for this series, so it counts. Those three have handled demons, powerful psychic humans, and the lord of the netherworld. They win without me lifting a finger.
Second team! Jack of Fallout 1, 2, and 3. That's right, the Vault Dweller, Chosen One, and Lone Wanderer. There's know way that this three of a kind can fail. The very people who take out super mutants, deathclaws, and Enclave soldiers with ease.
Third team! Megabyte, Hexidecimal, and Guardian Bob from Reboot. Assuming I can keep everyone from backstabbing each other (entirely possible, given the circumstances), this is a winning combination for sure! GAME OVER...
Team number four! Ash Williams (Evil Dead games), Duke Nukem (Duke Nukem games), and Serious Sam (Serious Sam games)! So much ammo and one-liners, so little time... Not only would hell freeze over from awesome, but it would also be funny!
Fifth Symphony team! The Main Characters of P3 and P4, plus Aigis during "The Answer". Three characters, all with the wild card for Persona summoning. I think you can see the possibilities. God, what a mess on the walls...
Sixth team...
There was a game! It counts!