Go for EVGA card. check the comparison below to see why I'm recommending this card.
EVGA GeForce GTX 780 3GB SC ACX
Core/Base Clock = 967MHz
Boost Clock = 1020 MHz
Price = $484
ASUS GeForce GTX 780 3GB DC2 OC
Core/Base Clock = 889MHz
Boost Clock = 941 MHz
Price = $519
I usually recommend EVGA cards for better performance, better cooling and excellent customer support service.