CoD has a very boring storyline, 1 shocking scene that causes uproar in newspapers across the country (You know, for teh lulz), and rehashed content. It's pretty much half assing it through the single player, and cashing on the multiplayer.
Battlefield 3 comes from a company thats idea of stopping people from buying the game is to make a mandatory program that must be downloaded and installed to play BF3, and the kicker is... wait for it... They want to scan all of your computer. Your files, videos, music, browsing history! YAY FOR INVASION OF PRIVACY.
The simple fact is, while the game play is tolerable, the companies who make them are not.
If you buy battlefield 3, you're telling EA "Don't worry about my privacy, I don't need that, keep making origin mandatory!"
If you buy CoDMW3, you're telling Activision "I don't care if you just cut & paste your stuff, i'll still pay £30 - 40 for your game! oh... whats that? Do I want to pay £10 for 4 maps from a previous game? all you did was put them into a downloadable file? YEAH! WHY NOT!"
Support either company, screw over gamers.
Done.