Gears. I never got to play Call of Duty 4 really and I'm never gonna really get a com to run it so I'm not really interested in it anymore. Despite the fact I vowed to play that game on my own PC one day.
Besides, seems like a new game already came out.
Anyway, I liked the first gears for the first 2 and a half acts I played. I have yet to play the 2nd half of it and the second game but I like the atmosphere of the first so I choose Gears.