Team fortress two, purely because it has class's that work together.
The best you will get with COD4 is a sniper trying to cover his ally's, and even then that tends to fail seeing as you die in 1-5 shots, or a single grenade, or a single c4, or a claymore, or a headshot... you get the picture.
Its just that team fortress has class's that are designed specifically to have weakness's and strengths, where COD4 was not.