Long time since we saw one of these. John Carmack, head programmer at id software, has always got something interesting to say about the present and future of 3d chips, this time he discusses and compares the GeForceFX and ATI's R300.
Things seem well balanced at this time and perhaps will continue like this unless one of the two companies pull some really improved drivers (more likely: NVIDIA) or get some prices cut on place (more likely: ATI)...
At the moment, the NV30 is slightly faster on most scenes in Doom than the R300, but I can still find some scenes where the R300 pulls a little bit ahead. The issue is complicated because of the different ways the cards can choose to run the game.