Chaos, the term "best" is pretty subjective and all depends on what perspective you view a video card from.
Is your primary concern FPS? If yes, then my guess would be a NVidia card.
If you are more concerned with image quality, then I would opt for an ATI card (Radeon or higher).
But then we get to your video display. What kind is it? If it is a low end monitor, then image quality may not be noticed between the ATI or the NVidia.
Pretty difficult question to answer. I do not think there is a "best" video card out there on the market. I think there are cards that will fit your needs, but "your needs" are just those.