Pass on the XFX if you can. It might be a bit cheaper but there's a reason.
I have two XFX 7850's, and I wish I'd done some reading about them before I purchased them. From what I understand, XFX uses cheap MOSFETs and VRM circuits, and unless they changed recently, pretty lousy cooling. My 7850's run really hot and can't even handle the suggestion that I might think about overclocking.
Granted, they don't run so hot that they have to throttle to protect themselves, but my computer is under my desk, and after a couple hours of gaming, my legs are sweaty from all the heat being dumped out under my desk.
I've never owned an Asus but I have a couple friends with Sapphire hardware and they all swear by them.