for the same other configurations like processor and ram and storage . the 780 is superior to the 770 and slightly lil bit better than the r9 . but consider the budget .because the 780 is way too expensive . the r9 is the around the same price as the 770 and offers the same performance as of the 780 . so consider that
also consider that r9 generates heat more than the 780 . that will not make much difference since you are building a gaming rig and you will install good quality cooling system . those high end GPU'S need that
so short answer : performance wise the best is the 780 . budget wise the best is the r9
though if i were you i'd wait till October .because the new Maxwell cards from nvidia are coming out around october