$500 gives you some attractive selections.
Are you wed to AMD or would you consider nVidia?
The new AMD R9 cards are pretty amazing, but pricing has gone through the roof due to their popularity with the Bitmining crowd. Based on that alone I wouldn't consider a R9 card until pricing gets back in line with where it ought to be.
If I were spending my own money with a budget of $500 or less I'd buy one of these;
AMD R9 280X Club3D RQ - $469.99 + free shipping (NewEgg)
EVGA GTX 780 ACX - On sale at NewEgg for $509.99 minus $20 rebate card - $489.99 + $5.92 shipping
If you want to go best bang for the buck consider this;
Gigabyte GTX 770 - $339.99 + $5.92 shipping (NewEgg)