Nvidia does a lot of their driver and other software development with Linux (as well as chip design) so they have to make good drivers for Linux... (at least for themselves if not for the whole Linux community ;^)
Call me old-school, but I have always preferred OpenGL to DirectX/D3D. Maps and models rendered in GL appear more solid to me, while things rendered in D3D seem paper-thin or hollow. And Nvidia was doing OpenGL really well for gamers back when they released the Riva-128 (1024x768x32bit on 1 chip while 3Dfx Voodoo2 was doing 800x600x16bit on 1 chip or 1024x768x16bit on 2 chips) and have gone strong since.
ATI didn't start doing good 3D until the Radeon. I have friends who swear by them (in Windows). I have only installed a couple Radeon cards, 1 for a friend and one at a computer shop on a linux box. The latter being a 9600 on Mandrake 10.0... I forget driver version but it was from this last summer. It performed rather horribly and with many rendering problems. Performance in 1024x768x32(24)bit was dissappointing and it mis-rendered shadows in GL apps. It also did not make use of advanced rendering such as bump mapping. FSAA was not enabled, nor was anisotropic filtering.
The programs used were 'foobillard' and 'celestia'
That was on a P4-2.8 with 1Gig PC-3200.
By comparison
A GF5700-Ultra on an Athlon-XP 2.6 with 512M PC2700 renders those same apps extremely smoothly at 1600x1200x32(24)bit while using FSAA-2xQC and 2x-Anisotropic. Bump mapping works perfectly.
My old Geforce3 card ran Quake3 smooth as glass in 1600x1200x32 with high details on and trillinear filtering (no FSAA though), in Windows it got choppy if I took it higher than 1024x768 (still no FSAA).
... just my $0.02 ... er, more like $0.20
btw... the Radeon I installed for a friend was an older 7x00 series or so. I did not benchmark it or test it out much, just made sure the screensavers worked.
