The GTX650 is the better of the two, and probably has more compatibility with games (I could be wrong though, I don't run AMD's very often). Either is fine for most Adventures.
The only major difference between Nvidia and AMD , is Nvidia has a couple of propriatery technologies that AMD does not . PhysX being the most prominant example . In a game with PhysX , if you use an Nvidia card , you might see a butterfly or a vapor trail of a bullet flying by . With an AMD card , you would not . Even then , the differences are ratuer irrelevant , as there are not very many games that contain PhysX anyhow .