I chose Call of Duty. Though I've mocked and poured scorn on people who played it before, I'm a lot more mellowed out in my ripe old age of, err, 28. Now I just want to turn off my brain, spray my P90 everywhere and be told how great I am, and CoD is currently the best game for me to do that. I'm even enjoying Zombies, which I never thought I'd ever find myself saying.
Honestly DOOM would have to be my top shooter game. I just think the overall graphics and several different weapons of choice are fire. Logitech G has some pretty dope suggestions on Top shooter and FPS shooter games too.