Arcturus314 :
Like others have said, probably R9 290. If you want a bit more power go for a 290X or 780 Ti
The R9-290X averages roughly 6% better than an R9-290 (depending on game sampling) but costs $100 more.
The GTX780Ti averages about 15% better (comparing top-end models to be fair) but costs $250 more.
Put another way, comparing top-end cards with the R9-290 at 100%:
R9-290 ($400)
R9-290X ($500) + 6%
GTX780Ti ($650) + 15%
So the GTX780Ti is over 60% more money for 15% more performance. Ouch. I'm comparing top-end cards of good value not random cards.