If this is a fair fight, ie brawl, no weapons...
Lets have some Tekken boys out: Brian, Violet, and Law... and that's all I'd need.
With weapons, but no guns...
I'd have to go with some of the Soul Caliber characters: Mitsurugi, Nightmare, and Yoshimitsu... I know he's really from Tekken, but it wasn't a bad crossover.
"Namu! Namu! Namu!"
And if we're going the whole hog and making this a bit of a war, ie with guns...
I think I'll have to be shameless and take a Force Commander and well kitted out Tactical Squad from Dawn of War... Space Marines Win All!!!
But if I have to have specific characters I'd take: Master Cheif [but who wouldn't], The Cole Train [he's the best guy in GoW], and you need some eye candy and a sniper, so woot retro Sniper Wolf [for shame my boy, for shame]...
Can y'all deal with that!!!