Well, playing BF3 online at minimum settings still looks absolutely gorgeous, but it is a bit of a system hog... I'm running an AMD Phenom II X4 810 with 4GB of DDR2 and a Radeon HD 4850, and to get over 40fps I have to play it on minimum.
However, if system requirements are something you've already considered, go for BF3. All issues of which game is better aside, BF3 has populated servers any time of day or night, and the community is much more supportive than MW3's community, which I have nothing against, but the amount of kiddies raging there day and night gets seriously annoying.
