Which card is a better gaming graphics card for my pc?

I'm just trying to get an honest opinion of which gpx card is better...

ASUS 2GB GDDR5 DIGI+ VRM technology Graphics Cards HD7770-2GD5 or

Gigabyte GeForce GTX 650 OC 2GB GDDR5 PCI-Express 3.0 2xDVI-D/HDMI/D-SUB Graphics Card GV-N650OC-2GI

OS Version: Microsoft Windows 7 Ultimate, Service Pack 1, 64 bit
Processor: QuadCore AMD Phenom II X4 910, 2571 MHz
RAM: 6143 Mb
Graphics Card: NVIDIA GeForce GT 430, 1024 Mb
Hard Drives: C: Total - 953766 MB, Free - 753636 MB; D: Total - 610477 MB, Free - 1870 MB;
Motherboard: XFX, MI-A78S-8209
500w power supply
Antivirus: AVG Internet Security 2014, Updated and Enabled

Any help would be great.