So after playing for about 3hrs last night I have to say I like MW3 a lot more. BO2 seems a little cartoony to me. the knifing system is a little weird to get used to. But there are a lot of cool new attachments and killstreaks. ATM I am using Type 25 AR with red dot (with blue circle crosshair) and adjustable stock (stalker pro perk in MW3) with lock on missile launcher (forgot name, 2nd one you can unlock) and the 3 original Perks you start off with.
I will mostly play MW3 for multiplayer and BO2 for zombies, that is all.