Which is better?

Personally, I'd play MW3 over BOPs any day. When I first bought BOPs I was expecting a revolutionary code experience but I was shortly saddened by the ridiculously low frame rate I was getting and regardless if all the graphics were set to low I only got around 60 fps. Apparently they had patched it but it still runs slow for me whereas MW3 runs completely fine. BOPs isn't a good game, in my opinion. MW3 could be defined as a rehash of MW2 but I still enjoy the game a lot. There's new guns, perks, maps, killstreaks, gamemodes, and a new playing experience pretty much; it's more gun-to-gun rather being loaded with killstreaks. If you're choosing between any CoD I'd recommend MW2 though.