The gtx 770 and the r9 280x perform about the same with the gtx 770 coming out a little ahead. They are pretty much tied though since game developers design games based on either AMD or Nvidia. For instance, the r9 280x would run BF4 better than the 770 but the 770 will run batman arkham city (or the new on that hasn't been released yet) better. I have had both AMD and Nvidia cards, both are great but I find the Nvidia driver software a bit easier to work with.
If like Nvidia better or trust their reputation then yes get the gtx 770, otherwise either one would be great.