A riva 128zx is a good choice chipset for what you have, and they are really cheap.
You could goto a faster card such as a tnt, but the differences on your speed of a system is not that high. This was like voodoo2 when it came out. They are scalable cards that work better with faster machines, but should be fine for what you have. There will not be alot of diff between them and their older chipsets though.
I have installed and Uinstalled both a Banshee and a Voodoo2 on my 233mmx. The voodoo2 ran significantly faster and smoother than the Banshee, especially with some of the newer games such as Shogo. So if you are looking to get a gaming card don't sacrifice because you don't think your machine can handle it.