Sorry but Wreckage, a self admitted fanboy, calling someone else a fanboy?
ATI has a slight edge in image quality and they have HDR+AA (which only Oblivion has and through an unofficial patch). ATI also has better AA algorithms in that they cause less of a performance hit. ATI also runs better at DirectX games. nVidia runs faster in OpenGL games and is a fast card overall, especially with no AA but once you start cranking up the features it starts falling back in line with ATI and even behind it. In truth, when you buy a $300-500 video card, you want to crank up the features and resolutions. nVidia does have a better dual card implementation but I feel that SLI and Crossfire are not worth the money as they do not provide a 100% speed boost for 2x the cost. One thing to note is there are a lot of newer high profile games (games like FEAR and Oblivion) that seem to be shader heavy which ATI has an edge on nVidia. But in the end, it depends on what type of games you play most.
As far as noise goes, the 7900GTX is supposedly near silent. Silent enough that the noise on the X1900 series is noteworthy. I've been using a X1900 recently and running RTHDRIBL to try to stress the video card. With no other sound but the ambient noise, it was clearly audible over my case fans but it wasn't to the point where it was annoying. If it was slightly higher pitched or slightly louder then it would get into the annoying stage, like when the fan spins to 100% during computer startup. This is a YMMV issue. Though one has to factor in that when you game, you usually have a game running or headphones on. I found that during gaming you don't notice it except at very quiet moments.