Well, I'll just say this:
When my GeForce4 4600 died after a year and I got it RMA'ed for a new one, I installed my Radeon 8700 card and EVERY damn game had graphics glitches. Tried everything I could to fix them, but all my games had weird clipping errors, NWN's cursor blinked constantly, and in Arx Fatalis, it would crash.
I would personally stay away from Radeon, since most DirectX Game makers make use of the nVidia chipset more often than not.
BTW, the LATEST GeForce card has left that huge honking fan design, and now is back to normal. (When I saw that, I laughed). When you are looking to buy a video card, look at the cards other features besides just speed. Look at the shader support, the different DirectX plugin's it can use and such..
Radeon says that it supports DirectX 9, but that is such a marketing ploy. NO GAME YET offers fully blown DX9 effects. So it's like buying a car that can fly, but the skyway isn't built yet.
I will stick with whatever card has the best overall speed AND the most compatible with games, and has advanced shaders.