Honestly it's sort of hard to choose. I'd probably go with the CPU/MOBO like jmsellars said. My reasoning is that this will mean you have a CPU to last the next few years, and also the motherboard will be a good setup for a videocard update. I think it's generally a good idea to get a new MOBO first. That way you can easily have the availabity to upgrade to a new card (or multiple).
Only downside is that your graphics wont be insane when playing BF3 Alpha. You could go with graphics if you're really wanting to get full/max performance from the game, but otherwise multitasking/adaptability comes first in my book.