MW3 will outsell BF3 no doubt about it, But from a technical standpoint BF3 is / will be better in every way. (Graphics, audio, destruction, vehicles ect ect)
But i respect COD because its an extremely fun and addictive fast paste FPS like no other. No other FPS game that iv played is as fun and addicting as COD. It will always keep you coming back for more...for example i played MW2 on a weekly basis all the way till Black Ops released...Killzone 3,Crysis 2,Homefront ect ect...i played those games for about 2 weeks till i just lost the will to play it again...
I will be getting both BF3 and MW3