It matters on the game as some prefer nvidia or amd but the 770 and 7970 perform pretty similar with one some times being slightly better. So what games and resolution u playing at?
Also atm the 7970 goes for like $320-400 where the 770 is still at $400+. Also the 7970 comes with never settle forever with 3 games of ur choice.
I recently bought a 7970 and my choice to get it over the 770 was the games it came with, which was crysis 3, bioshock infinite, and FC 3 blood dragon, which was the never settle reloaded and I paid $420 instead the $335 it costs now lol
Look up benchmarks for both and the games u play and make ur decision and does the games that comes with the 7970 help ur decision or not along with pricing