The Xbox is reasonable because it has good graphics and cpu power, and a really established set of games, in particular, Halo 3. The PS3 is the most powerful, but its expensive and the game catalog is still lacking. I would recommend getting Wii because although it has the least amount of processing power, the games and game play are by far the best. I would recommend something like medal of honor.

The xbox 360 might work since you can buy a mouse for it -- FPS games are much easier to control with a mouse (and keyboard) if you can get it.

I have the Playstation 3, and Resistance:Fall of Man is an amazing first person shooter with stunning graphics and great gameplay. I think this system is great for these types of games.