http://www2.hardocp.com/article.html?art=NjQ0LDQ=

ATi VS Nvidia In Image Quality:

In our in-game evaluation, we did not notice any differences in image quality. However, when we started poring over the screenshots, we did notice some differences. If you look on the floor to the right side in the first comparison above, you will notice that the ATI Radeon X800XT-PE has slightly more aliased floor lines than the BFGTech GeForce 6800Ultra OC

Resolution:

What we noticed immediately is that DOOM 3 looks incredible even at 640x480! And as we increased the resolution, the game began to look more and more like a pre-rendered movie......That's correct. We found that increasing the resolution, up to 1280x1024 and 1600x1200, was simply a better alternative than using antialiasing