Cosminrules is right about the drivers, and games generally run better on nVidia hardware (interms of consistent performance where the framerate isn't up and down all the time and interms of rendering correctly without glitches). If you go with nVidia, I'd recommend either saving yourself £50 on a GTX660 (since it's barely any slower) or putting an extra £50 on it for a GTX670 (since it has a considerable performance lead). The GTX660 Ti is a bit pointless when it's priced exactly half way between the GTX660 and GTX670 yet performs much closer to the GTX660.