At this point the performance numbers tell a pretty simple story, if it's raw speed you are looking for, the GeForce 2 is your choice. There is very little performance drawback to running your favorite games in Linux instead of Windows with this card. It provides a truly impressive performace across the board. The Radeon's performance will almost definitely improve as the DRI drivers mature, but for now, especially for the impatient, it is simply not a good choice for the hard core 3d gamer.
If, however, you are a graphics designer, and want a card with impeccable 2d image quality, with 3d graphics only a secondary priority, the Radeon is your best bet. The DRI drivers, even in their current state, are quite usable. For 2d only users, XFree86 4.0.2 provides production quality 2d drivers. The GeForce thoroughly trounced the Radeon in the Xmark performance test, so if you aren't running at a ultra high resolution, or aren't that picky, the GeForce is once again a better pick.
Now for my own input. The Radeon is a pretty amazing card. It's what I use, and I have yet to see a game that needs more power than the Radeon is able to provide. However, the OpenGL renderer for the Radeon is buggy, although the only games I've seen that suffer greatly are Loki Software's Heavy Metal (which is, regrettably, unplayable) and Soldier Of Fortune. Hopefully the people doing Mesa for the Radeon will fix this very soon since the Radeon is the best option for people who don't want to rely on the closed source, proprietary GeForce.
Now about the Voodoo cards. Unfortunately, 3dfx was bought out by nVidia, so these cards are a dead end market. If you're out to play the bleeding edge games like Rune or Tribes2, you'll want the Voodoo 3, 4 or 5. Preferably the 4 or 5. I think the Voodoo 5 is basically a Voodoo 4 with a second processer. However, this processor is not utilized by the Linux driver, and rumor says that the Linux 3dfx driver will never support it. So as far as Linux is concerned, the Voodoo 4 and 5 are the same card. All the drivers, Glide2 library and OpenGL renderers for the Voodoo cards were open sourced by 3dfx before they when under. It is an embarrasment to the Linux and open source community in general that this company failed.