So far the only arguments I've seen is "OH EM GEE THIS AMOUNT OF PEOPLE CAME FOR MW3 AND NOT BF3" and after that the arguments are strictly people BITCHING back and forth without any proof.
Both games will be good. I prefer BF3 because I enjoy the larger maps and the gameplay, but others enjoy MW3 for their reasons as well.
You can't compare the amount of people who are buying the games in the games quality as well, CoD OF COURSE has a larger following, it came out before BF even started to try to compete, and it's a different style of FPS, MW3 will be faster paced, BF3 will be about following orders and strategy.
Stop using quantity for your debates and use quality. Compare the statistics on each gaming engine on the same computer, etc. That's the only way to really tell which game is better hardware wise.