The Radeon is reported to have problems with 16-bit color games, such as polygon gapping and seaming, and visual snow. I've read that in several reviews; it is apparently especially prevalent in older games.
The Voodoo 5, otoh, is--like the entire Voodoo line--probably the most compatible video card around. I've had plenty of problems with my Geforce SDR through the many, many Nvidia driver iterations, but I can't remember ever having a problem with the Voodoo 3-3K that's in my second machine, or a while back, with my Voodoo 2 SLI cards.
As for bleeding-edge speed, yeah, the Geforce GTS and Radeon DDR will get you slightly better framerates in certain games at 16X12 resolutions, but for me the sweet spot is 12X9 or 12X10 resolution, and all 3 cards can handle any game on market at that resolution. The Glide compatibility is an important bonus, as I play a lot of UT, Tribes, and Unreal-engine games (Rune, Deus Ex, etc.). And the anti-aliasing features can really bring older games to life (as just one example, Darkstone is limited to 640X480, but with 4XAA, it really looks gorgeous).
That said, if I only played Quake 3--as most of the hardware review sites seem to do--I probably wouldn't get a 3dfx card as a first choice.