I have played both games for many hours and I would have to say my fav would be Halo. The campaign is super replayable and it's a way better party game.
halo does have a pretty good campaign, but the online play is way better.
Liked CoD2 online till white walla and satchel whores came in.
CoD3 online was the best whee
WaW was fun for Zombies and story.
MW2 killed it for me.
Black Ops zombies was really fun.
I liked Halo more in General.
Halos campaign of course.
Halo 2 online.
Halo 3 campaign.
ODST firefight.
Reach campaign and firefight.
I thought halo was everything that means xbox 360 and live... But then I played COD black ops and my life changed.
I def like Black Ops more since it is def more difficult and takes strategy. Halo does too, but I seem to kick a** really easily. In black ops I feel like I actually have to creap and plan sneak attacks rather then just running up to someone and perfectly aiming my sticky. Boosh!