I love both, but Halo 3 is better. COD 4 has no level system, so you are playing(like Halo skill) so you are not really being matched with like skill levels. COD 4 has levels which come with perks, so for a while you have an actual disadvantage. It also gets quite tedious after a while. Halo 3, while great, can be much more frustrating. It often centers around gaining an early advantage(usually over a specific location or weapom) and holding it. COD 4 tends not to have that problem(except in specific game types) I liked both a real lot, they are very different. Most people like one or the other way better.