Are the cache or original media files best placed on an Nvme ?

The original media files. Here's why:

The cache files are typically much smaller in size than your original media files. And NvME SSDs usually have no faster small-file random read/write performance than their SATA counterparts. So there will be virtually no difference in performance whether the cache files are on a SATA SSD or an NvME SSD. Both types of SSDs are way faster in small-file reads and writes than any spinning HDD.