A cache of ram is where data is stored in a faster Static Ram(SRAM) for ready access as opposed to repeated access using the slower Dynamic Ram(DRAM) since that same data is accessed by various programs. You can read more on cache at http://www.webopedia.com/TERM/c/cache.html
Regardless of chipset(SIS, NVidia, ATI, etc.) you would go by the type of card there. If you were looking over cards for a PCI-Express 16x board you would choose a model that supported 16x instead of one that was limited to 8x graphics. The differences seen between cards are often those seen when tested for gaming. ATI gets high marks on their high end models while NVidia sees good reviews on the mid range cards. Performance and budget are the two main things in choosing any compatable card.