Should i buy a evga geforce gtx 550 or galaxy geforce gtx 460

No question about it, the gtx 460 768mb is definitely the faster card and the better buy.

Google it, check toms charts, check anandtech etc. you will see it is a good amount faster. And the 460 has a huge overclocking head room, its stock clocks are relatively low at 675, I used to have a 460 768mb and had it at 920mhz. It was nearing gtx 470/560ti levels and it was still quiet and cool. As long as you arent planning on playing 1080p with full anti aliasing it is a great price/performance card.

EDIT: to clarify you CAN use the card to play 1080p but you may run out of memory since it is only 768mb if you turn up all the anti-aliasing options. But regardless it is faster than the 550ti which has more memory but wont really use it as well since it is slower.

just grab that GTX460 if the price are the same.