I have the Ati 9700 pro. It's really a good card. I had a few problems and a nice share of frustration to begin with, but most of it is sort out now.
I have been hanging out on the main Ati forum <www.rage3d.com>, to get that done, and have picked up some info on the way. There are problems with some games and Ati cards, but it isn't really all that bad. Some games get hotfixed drivers, but the that's very few. Neverwinter nights was the last one to get a hotfix, but very few games need them.
Mostly, the intial problems can be fixed, if you install the drivers correctly, don't use the APIC (to get 200+ IRQ's) on Nforce2 boards (quite nice that an Nvidia chipset has compatablity issues with THE leading competitors top cards, isn't it?), run DX9.0 (or higher), have a proper power supply, and if your MB is a bit greedy with the apc controller voltage, then increase it a notch. In cost/performance analysis, Ati it blow Nvidia cards away. However, you got to be real careful when you install the drivers. It is a process that can go wrong all to easily.
Regarding the Nvidia FX cards, I wouldn't buy them. First of all, Nvidia has been exposed of building cheats into their drivers so they report higher values in benchmarking programs, than the cards can really generate. I would think that it is proof enough that the dude that exposed them was confronted by Nvidia lawyers that told him to clean out the info on his page or face legal charges, and he said screw you (well not quite, he did remove something, but most of it is still there) and they didn't do a thing after that. But if isn't proof enough, then just rename the benchmark executables and see for yourself.
Furthermore, by ready for a lot of noise from an FX card, or to invest in a more silent fan for your new card. Some of them produce more than 50Db of noise! Lastly, some of the FX cards can't sustain prolonged use of GL screensavers. I can't remember the company that did the test (if anyone asks I will try and find the link again), but they tested 5 cards or so for 24 hours and 3 of them fizzed off. The cards switched the GPU fan off, because they thought the system was in standby/hibernate!!
Alas, it looks like you can't get GFX cards without drawbacks these days. I recon it is a consequence of the heated GFX card war between Nvidia and Ati (like Voodoo and Nvidia was had it), but you can do the research and buy the card that gives the best value for your money. As a fanatic fan of my previous Nvidia cards (Guillemot maxigamer TNT2 Ultra and Asus Geforce 2 Ultra, totalling over 3 years of enjoyment), I now vote Ati.
It's only after we've lost everything, that we are free to do anything.