Maybe I'm losing touch with the DRAM market... I've never heard of PC-RAM - I presume you mean PCxxx SDRAM, like PC100 SDRAM, PC133 SDRAM...?
Which is better? VC-SDRAM is faster, but more expensive. It includes some registers on the memory chips that act essentially as localized SDRAM caches thus speeding up some memory operations. In the best case, VC133 SDRAM can be 10% faster than PC133 CAS3 SDRAM, but in real life I've seen more like 4-5% faster. Whether this is worth the extra money is up to the buyer.
There are some limitations on which chipsets support VC-SDRAM, and I'm pretty certain that you can not mix modules (ie. 128MB PC133 SDRAM in one slot, and 128MB VC133 SDRAM in the other), but I've never tried so I don't know for certain.
