Battlefield 3 or C.O.D.:Modern Warfare 3? Your choice.
I still like COD. I never did like Black Ops or World at War but I am a fan of the Modern Warfare series and the original.
That being said, Activision signed it's own death warrant when it came up with the brilliant idea to release a COD game every single year. I don't think Bobby Kotick knows what he's doing. He's expanding the company, which is fine, but he's putting too much resources into a few selection of games. Too many chefs to piss in the pot isn't going to make it taste better. If you look at the MW3 trailers, it's too mashed and mixed. It looks more like Black Ops mixed with Modern Warfare, which might be fine for a little while but it's going to lose appeal very quickly. Why? Because you've played both games already and you don't want to get the same game(s) again. They'll still make a billion this year though.
Battlefield 3 will likely be refreshing. It won't overthrow COD now, or maybe even ever, but it seems to be on pace to be for the gaming community what COD4 was for the gaming community.