For my money, I'd be getting an Xbox 360. Reason being is both have great graphics, if one is slightly better then the other I don't care, my PC beats them both anyway.
Where the Xbox shines is in the multiplayer aspect. The level of integration the xbox operating system has with it's games is excellent. If I didn't have more important uses for my money I'd be picking up a 360 for sure, just for the online play.