Because I have used an exhaust of reasons why I'm to prefer BF3 over MW3, I'll use a new one I've just thought of.
We have two multiplayer-heavy shooters. One releases a beta to try and iron out bugs and get feedback from the community. The other had a prequel that released with an obscene amount of bugs due to lack-of-beta, and still did not host a beta this time around. You make the call.