my current graphics card is an nvidia geforce 9800
It was not too expensive and it can run any game I throw at it at full settings.
However, it will occasionally crash and it runs really damn hot.
Also its a power whore, I had to upgrade my psu for it.
I have never had any problems with my other computer running ATI graphics, but I get the impression that the nvidia one is better for the price, despite its faults