gtx 770 is efficent can be sli'd and cheaper
7970 is better value more games but uses more power and cant be crossfired due to micro stutter.
Correction: Has issues when CrossFired. You can still do it (I do), but you will run into issues, and you won't get as much performance as you would like. That said, the recent 7990 article confirmed that AMD is working on a solution to the CrossFire micro stutter issue.
Overall, I would recommend the 770 over the 7970, unless you would otherwise purchase the games from the game bundle separately. I just wanted to clarify that CrossFire, though very buggy, is not utterly infeasible and that the current issues may be resolved.