Which GPU is better ?( need help)

Hey guys I have Finally completed my build  

except for the GPU   ..

I'm planing to get one of these two :

XFX Double D HD 7970 Black Ed. 3GB

AND

EVGA GeForce GTX 680 SC Signature2

so which one is better and what would you recommend ?


and BTW this is the rest of the build ( if it matters ) :

Gigabyte GA-Z77X-UD3H
Intel Core i5-3570K
Cooler Master Hyper 212 EVO
Corsair Vengeance 8GB (2x4GB) DDR3 1600 MHz
Samsung 840 Series 2.5 inch 120GB SATA III
Cooler Master HAF 922 case