You would have to provide more info. What games are you planning to play in the upcoming years? What resolution are you using?
If you play in 1080p, I'd get the 760. For instance, my monitor is 1920 x 1200 and I plan to get a 760 for myself. I currently use a 460 and so far it's been handling games surprisingly well, this is why I have a feeling that anything above a 760 would be overkill for those resolutions.
If you use 2560 x 1440 or above, then the 770 makes more sense. Or for people with 2 or 3 monitors setups, 2 x 770s in SLI might be necessary.