I slightly prefer Sculpey Souffle over Premo because the colors are trendier and the clay has a smooth texture that is never sticky. However, it's marginally more expensive and much harder to source than Premo.
Also, neither of these clay varieties noticeably shift in color after curing. The only exception is Sculpey Premo’s Translucent and White Translucent colors, which become much more yellow-tinted when cured. For this reason, if you are looking to create with a lot of translucent colors, I would recommend Cernit instead. Otherwise, these clays cannot be beaten.