If it has to be one and only one game, then it has to be a game that has hours, months, and even years of game-play to offer. I'd pick the new:
Mortal Kombat
I hope and pray the fighting engine is deep and competitive.
Umm.... I need console buddies. Getting "Super Street Fighter IV" for both systems day of release. I have and use headsets on both consoles. Gamer ID/Tag on both systems: bwinches