If the GTX 770 has 4GB and a higher clock, then that card is going to be the better choice. But at a performance/dollar ratio the R9 280X is MUCH better. The GTX 770 is not much faster than the R9 280X, and in some games that are optimized for AMD cards the R9 280X will actually do better. If you want the better card it would be the GTX 770, but if you want the better card as when it comes to price, and performance the R9 280X is a winner.
Since you already bought the 770 I would just stick to it , the EVGA ones are awesome and they have a great cooler on them, and the game bundle is pretty good. The 4GB version is also good for higher resolutions and multi monitor.