for my main old gaming PC (440BX) I currently have 3 usable video cards, a diamond stealth64 2001 4mb, which seems to be fine on DOS, but no win98 support (also it's 2d only), a 9500PRO, which seems to be good on windows, but not good for DOS, also I tend to think it's worse than average when it comes to CPU limited scenarios (I'm running a PII 400 but I will probably use a P3 soon)? maybe it's just placebo (caused in part because it's a reality these days when it comes to AMD vs Nvidia with DX11), or unfair to compare due to use of Glide with my Voodoo in some games vs D3D, but it seems to be the case.
and the voodoo 4 4500 pci, which is good on windows and supports glide which is great, but it's also bad on lower res dos games (gives me some horizontal line artifacts), I also have 2 Voodoo 2 8mb, but one is not stable and the vram limitation makes me unhappy with some games, so I kind of don't know what to use, most of the time I'm running the Voodoo.
but I'm thinking of getting a cheap FX 5200 and give it a go, the FXs are poor performers for DX9, but for older stuff they are fine, and I think it will be better at compatibility with dos compared to the V4 and 9500PRO I have, ideally I would get something like a 5600,5700,5900 but those are not as cheap and easy to find over here, and I don't intend to use anything faster than a coppermine P3 around 1GHz, so it's kind of pointless I guess.
I also don't see much point in going for Geforce 6 for windows 98, and specially not x800 series,
so while the FX series were not great back in the day due to poor DX9 performance, for older games they are looking like the best option considering availability, compatibility and performance.
but it depends on what you are targeting, I'm happy with 1024x768 and little AA/AF, also not running games newer than let's say 2001 (and if you are going for newer stuff I think XP is the way) and very few DOS games older than 93.