For any carbon wheel go with the manufacturers suggested pads first and foremost and if they really don't recommend anything like
cxwrench said SwissStop makes great pads (Black Prince and Yellow King) and make sure you are using a carbon specific compound and get the best you can, brake pads are the worst place to cheap out.
However keep an eye on those old wheels make sure everything is good on them. Never know what happened from that previous owner unless you really trust the seller.