I started out with a 3dfx Voodoo 2 card, back in 1997 or so.
Eventually I switched to ATI's Radeon 9800 Pro, although I had various issues with its OpenGL support and eventual death.
Since then I've mostly used NVIDIA cards (starting with the 6600 GT), and was especially impressed by the PhysX features when I played Mirror's Edge and Arkham Asylum. These cards haven't been without issues either, though, as a few of them have died or otherwise malfunctioned. (That said, my GTX 260 malfunctioning meant that I got a free upgrade to a GTX 460, so I'm not entirely unhappy about that.)
TressFX is making me curious about AMD/ATI cards again now, although I'm hoping that NVIDIA will start supporting something similar.