Hard to narrow down to precisely one card over twenty years of PC gaming, and no doubt some of the ones I could list are partly because of memories associated. So, I'll pick one for each team.
Voodoo 5 64mb. These were the times when you had to upgrade quite regularly if you wanted the games to be playable. I recall owning this for a little over two years before a new generation of games coming through which literally rendered it obsolete (Unreal 2 / Project IGI 2). Anyway, a great card and miles better than anything I had before. I can't recall what the vendor for the board was.
Asus Matrix AMD 7970 3GB. Quiet, around twice the performance of the previous card, nice image quality, and bought when a good deal was on. Brilliant. However, maybe I should have hung on to it a little longer before upgrading; I think I had it in my system for around two years.
KFA2 GTX980Ti. My current and longest-serving graphics card (4.5 years now). Pretty quiet, a fairly decent overclocker and rock-solid reliable. So, on the one hand, maybe this GPU takes the crown.
