My recommendation would be for one of these:
S3 Trio/Virge 2D card + 3dfx Voodoo 2
PROS: great balance of compatibility and performance for such a PC, very good performance at higher resolutions in all period correct games, including those that support multitexturing. Granted, the Pentium MMX 233 is not a very powerful CPU, but it does benefit in some games from faster cards. I have a Pentium MMX overclocked @ 292 MHz, and it's surprisingly fast when paired with a Voodoo 2 - games like Unreal are actually extremely playable (playable by "retro" standards 😁 )
CONS: the Voodoo 2 can be quite expensive nowadays, image quality is usually worse because of the whole passthrough cable situation + the fact that Voodoo 2 cards inherently have lower output quality, not to mention that S3 cards are also a hit & miss when it comes to image quality.
3dfx Voodoo Banshee PCI
PROS: great image quality, great compatibility - albeit not as good as the Voodoo 2 when it comes to old Glide games, you don't need an additional 2D card, performance is better than that of the Voodoo 2 in single textured games (but it's not that important, those games run great on Voodoo 2 as well), the card can be cheaper (~$60) if you're willing to wait & hunt for it.
CONS: performance is worse than Voodoo 2 in games where that actually matters (multitextured games that apply both a texture and a lightmap like GLQuake, Quake 2, Unreal, etc). In GLQuake, for example, the Banshee bottlenecks a Pentium MMX 233 even at 640 x 480 (and when the CPU is overclocked, the card becomes a bottleneck at 512 x 384).
S3 Trio/Virge 2D card + 3dfx Voodoo 1
PROS: perfect compatibility with early DOS Glide games, it has a "period correct cool factor" to it, the price can also be quite low if you're willing to hunt it down over a longer period of time.
CONS: performance is quite poor, additional 2D card is needed, the Voodoo 1 is a serious bottleneck for a P MMX 233 - it's more suitable for Pentium 166 or older, image quality is even worse than that of the Voodoo 2.
3dfx Voodoo 3 2000/3000 PCI
PROS: great image quality, no additional 2D card required, performance is top-notch in any game (as long as the Pentium MMX is also up to the task), suitable for an overkill Pentium MMX build
CONS: VERY expensive and rare, the card will be severely bottlenecked by a Pentium MMX (even when overclocking the CPU) - but this can be both a good and a bad thing depending on how you look at it, compatibility is not that good (there are some old Glide games that refuse to work with it and there's no known workaround).
That's... about it. As you can see, all my recommendations revolve around 3dfx cards, and there's a reason for that. 😀 Yes, there are some nVIDIA TNT/TNT2 PCI cards that will also work well with a Pentium MMX with the right driver, but unless you get very lucky those are also quite rare, expensive, & since they don't support Glide... MUCH less compatible for the 1996 - 1998 timeframe, so might as well just go with a Voodoo and be done with it. 😀
2 x PGA132 / 5 x Socket 3 / 9 x Socket 7 / 12 x SS7 / 1 x Socket 8 / 14 x Slot 1 / 5 x Slot A
5 x Socket 370 / 8 x Socket A / 2 x Socket 478 / 2 x Socket 754 / 3 x Socket 939 / 7 x LGA775 / 1 x LGA1155
Current rig: Ryzen 5 3600X
Backup rig: Core i7 7700k