Halo 3 and Call of Duty 4 are both good, But I prefer Call of Duty 4 Because it is more Realistic, and I just have more fun with the game modes. Halo 3 is the Same as Halo 2 but with added Stuff. I am still disapointed with Halo 3's Story line.
halo 3 has a lot better history with its story line, which is original as opposed to COD that uses real history. also, halo has a lot better online, along with different game formats like forge.
No way guys Call of duty 4 all the way hands-down because more people probably play call of duty 4 plus you can make your own clan and name it whatever you want it to be with your friends online and you can't do that with Halo And the best thing about of call of duty 4 is that you get more Firepower if you rank up