650<60<270. Both are good for gaming, if one was that much better than the other wouldn't be in business. Each card has their strength depending on how a game is coded, but they are more so equals. Nvidia does create a better overall experience with their software and drivers so I try to go with Nvidia when I can.
I just switched from a 460 to a 280x because at the time the 280x was a much better deal than a 770. It performs nicely but I'll definitely suck up the $20-30 and get nvidia again as I see a lot more random glitches.