I don't have much experience with XFX PSUs but I have heard good things.
I have had plenty of experience with corsair PSUs though, and have just used an RM550 in a mITX build I did. It has been fabulous so far. Excellent build quality, love the modular design and it is so incredibly quiet. I can definitely vouch for an RM series PSU.
Because if not, I recommend the S12G-550 (or 650): http://anandtech.com/show/7761/seasonic-s12g-650w-power-supply-review. It should be cheaper than the other options (in my country it is).