The 680 is the best of the 3 in performance but it depends on the game, the 960 has a lot of newer technology and produces less heat and uses a lot less power than the other 2:
If I had to choose, I would go with the 960 almost every model is silent during gaming while keeping incredibly cool, which I deem most important. But other people are different.
The 680 is the best of the 3 in performance but it depends on the game, the 960 has a lot of newer technology and produces less heat and uses a lot less power than the other 2:
If I had to choose, I would go with the 960 almost every model is silent during gaming while keeping incredibly cool, which I deem most important. But other people are different.