Search the forum for threads on DOS game compatibility, the original Voodoo Graphics is the most compatible, 2/3 somewhat, 4 isn't. So you could go for 4+2, but a v1 would be better.
Voodoo 2 DOS Glide compatibility matrix (linked post is voodoo 3 info, thread's original post is on v2).
If you don't plan on playing DOS games, just go with the v4.

I went Voodoo2 SLI as it seemed to be able to act like a a Voodoo 1 good enough for my games and had good enough Glide support for the later games as well. It frees you up to use any graphic card you want for more modern stuff

It all depends on your specific build.

My choice would be:
- Pentium MMX 166 or slower: Voodoo 1
- Pentium MMX 233: Voodoo Banshee PCI/Voodoo 2 (even a Voodoo 3 PCI would be a surprisingly good fit, particularly at higher resolutions with an overclocked Pentium MMX @ 266 / 290 MHz)
- AMD K6-2/3+ @ 500+ MHz: Voodoo 3/Voodoo 4 AGP
- Celeron 300A @ 450 MHz / Pentium 2 450 / Pentium 3 Katmai: Matrox G400Max or Riva TNT2 (Pro/Ultra) + Voodoo 2 SLI
- AMD Athlon / Pentium 3 @ 800 - 1000 MHz: GeForce 2 GTS/Pro/Ti/Ultra or GeForce 3 paired with a Voodoo 2 (Voodoo 2 SLI works too in this case but it would be overkill).
- AMD Athlon Thunderbird 1.4 GHz / Pentium 3 Tualatin 1.4 GHz: Voodoo 5 5500 (if you really want to use a Voodoo card), however a GeForce 3 / 4 Ti would be more suitable.
- Athlon XP: if you're aiming for a very flexible / time machine PC, a Voodoo 2 can be paired with another high powered GPU (like a GeForce 4 Ti 4600 / GeForce FX 5900 or 5950). Some people like to use a Voodoo 5 with such a system, but I myself think it doesn't really make sense.
- Pentium 4 / Athlon 64: no Voodoo for me on such a PC 😀

If its just dos games in general then the V3 or V4 isn't a bad idea as they are fast and compatible.
If you add dos glide games to the requirement, none are ideal, your choice will depend on which games you want and their compatibility.

Windows the V2 will allow you to pair with a strong D3D card and give you best of both worlds. Don't see much point pairing the V2 with another Voodoo unless a game refuses to work with the later cards
The V3 or 4 if your just after fast glide support.

What CPU does the PC have? if were talking about early P2 or below your already limited in performance anyway

V3s are the most compatible voodoos. But the general trick for voodoo compatibility is voodoo environmental variables and the version of the glide.ovl file. So generally a voodoo 3 for example can just run the Glide2x.ovl and then you are going to do Voodoo2 environmental variables and the game will treat it like a voodoo 2. There are probably only a couple games that only work with voodoo 2s though and they are windows games that are hard coded for voodoo 2.

Voodoo 3s can also run the few games that work only with banshees for example resident evil 2.

Voodoo2s can generally work with almost all games that are for voodoo1 with very few exceptions.

The exceptions are statically linked games that only work with voodoo 1s and there are only a few, and this is the only reason to ever use a voodoo 1 Example is a game like Dreams to Reality. However Voodoo 3s have less compatibility issues with voodoo 1 games than voodoo 2s, if that makes any sense.

Lastly if you intend to run V2 SLI keep in mind that even with two voodoos in SLI a voodoo 3 3500 is still faster can do higher res and doesn't have screen tearing.

TLDR: Voodoo 3s are the best
Voodoo 2 SLI though can be awesome when paired with a capable 2d/3d card like a Nvidia Geforce 2-3-4 Then you get the best of all worlds in retro gaming and you look cool while doing it.

Well, I have two setup options, one is Gigabyte GA-7IXE4 with Amd Duron 700MHz & 512 Mb SDRAM and the other one is QDI Advance 10B with Celeron 1.1 GHz & 1.5 Gb SDRAM. Had both of them laying around so I've thought I'd make a better use for them, even wanted to make one with Dos 6.22/Win98SE & another with Windows Millennium just for the fun of it; and just to add on to my primary question....in your opinion, which ATI card would be the best option to accompany Voodoo2 for 2D gaming ? I know people mostly say S3 or something similar, but honestly I've been more of an ATI fan all my life 😉 , but nonetheless your opinions are greatly appreciated.

Me personally, I am beginning to see the wisdom in a simple voodoo 1 setup with a fast D3D card. Especially with prices being what they are these days. The number of titles that really only work in GLIDE, and benefit much from a faster glide card, is pretty small. And as far as glide cards go, the voodoo 1 has the fewest issues you need to work around for the few titles that really do need a voodoo card. Most of the games that claim glide support are actually opengl and you can use a geforce or a radeon just fine.

I know there are some exceptions. For example, Unreal Gold disables a few effects for D3D compared to glide, but you can patch that.