Each have their strong points: The Gf2 GTS is faster at the lower resolutions (like below 1280) by a fair margin. The Radeon is equal to, or slightly faster above that.
The Radeon draws less power than a GF2 card, so if you don't have good case cooling and a 300W power supply, this might be a factor.
I've always hated ATI's drivers, however the Radeon has been somewhat better recently. There are still problems with some games and applications though. (Mercedes Benz truck racing comes to mind.)
A strong point of Nvidia cards is the many driver revisions and updates. A problem with a Detonator driver is likely to be resolved within a couple weeks. The newer drivers can also eek out a little bit more performance.
Overall I personally like the GF2 cards better, but the Radeon is perfectly fine. To be honest I haven't used or installed an ATI product because of their past record when it comes to drivers.
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bloom25
-MAW-
(Formerly of the)
THUNDERBIRDS