The 7870 is better value (and comes with the Never Settle: Reloaded bundle, dont forget that) but the 760 is the stronger performer. Whether the increased cost is worth the increase in performance is up to you.
I used to run a 7870 before upgrading to my current 7970, you can get get high-ish settings at 1080p in intensive games while still getting a stable 45FPS while playing. Obviously you will need to lower the performance killing settings like AA and Post-Processing.
7870's overclock pretty well too, you can get a fair bit of extra performance from them.