Quote: ATI's performance/price ratio might be better -- but NVIDIA's dev tools are vastly superior and their drivers range from about the same (D3D) to way better (OGL).
I second that. In May, my old nVidia video card got toasted. Since I only make 2D games, I asked for the cheapest card, which was an ATI.
However, my game, while 2D, still uses OpenGL for better rendering and blend modes. And, well... The OpenGL driver for my ATI video card does not implement everything, and there are a couple of functions that do not work anymore. However, you might want to develop your game for the lowest common denominator to make sure it runs everywhere, so that is not necessarily a bad thing.