Silk is a fiber, satin is the type of weave. You can get satin in silk, nylon, polyester, etc. If the fiber used for the satin is cotton, then it's called a sateen. Confused?
The best choice for hair and face skin is a silk pillowcase in a satin weave...which to confuse you further, is usually called charmeuse. Dupioni isn't a satin...it's the natural looking silk that has slubs and a low sheen, which while it looks very nice, won't produce the nice results for the face/hair that a good silk charmeuse would.
If you get a silk charmeuse pillowcase, look for a momme (mummy, MM) weight of 19-20 or higher. Anything lower and it won't be very durable. There are lots of 16 mm charmeuse pillowcases out there in big-box linen stores that will just waste your money. I've had good luck buying silk on eBay directly from vendors in China or Hong Kong.