1. Vehicles - COD has no vehicles and that alone makes it lose points in my books. On the other hand, Halo vehicles execution are done quite well.
2. Gamplay tactics - I see Call of duty 4 as more of duck and cover, sneak around kind of game. Kinda like counter strike evolved... Where halo 3 is just all out chaos and war... I preffer all out war.
3. Weapons and power ups - Both have cool weapons but I prefer the mix and match of Halo.
Single player mode does go to COD4 tho...
Anyone care to share why they preffer one to the other? And please...no "Game 1 sucks a$$ while game 2 rules!"