Only current card which is heads and shoulders above competition in terms of raw performance is the GeForce2 Ultra. It's also a very safe choise compatibility-wise, Nvidia's drivers are of highest quality and updates are frequent. However, GF2 Ultra isn't the absolute best choise for gaming because of it's horrendous price, which as performance, is also ahead of competition: $450-$500.
IMO 64Mb ATi Radeon would be the best gaming solution of current cards on the market. It has the most complete feature set, superb 2D image quality, best DVD assist on the market and it's priced reasonably compred to the GTSU.
For MMORPGs you'll propably want Full-Scene Anti Aliasing support. In that respect Voodoo5 5500 and GF2U are excellent choises. Voodoo5 because it's FSAA - being 100% application-transparent - is without a doubt the most game title compatible. GF2U because it's the only card powerful enough to run just about any game in resolutions above 800x600 w/ 4-sample FSAA enabled.