You can choose at most three.
For me in order of importance....
1. Call of Duty : Modern Warfare 2
2. Halo 3
3. All wide-roam games because I can't choose XD

COD because it's completley epic and a great co-op shooter

Halo 3 because I own and could destroy you all (No I dun have my own Live yet)

Wid roam games, because it gives a wide variety of skills, and it allows you to explore and conquer.

What are yours and why?