Write once (NOT Re-writable) CDs are your best bet for longevity, apparently. They should last several decades. Stored correctly, of course!
Worst would be re-writable DVDs.
For serious long-term archiving of important data, the professional approach is to keep copying from existing media to next generation media - that way the data is constantly being checked and refreshed, and the storage medium is keeping pace with technological change.
SD