Personally, I have very good experiences with FLASH, and very bad experiences with spinning disc HDDs, CDROMs, DVDs.

IMHO, all long term cold storage is not reliable. Better to go with mid-term storage, and not just using one technology. For really important data, I would go for LTO AND BD AND SD card and maybe some paid online storage.

Flash data retention is about 10 years. And with ROHS everything is a smoking gun.