Depending on how long term you are considering, the other factor is whether the storage interface will still be around when you do want to access the data. Floppies and zip disks were prevalent twenty years ago, but not so much now. Cloud storage like Amazon Glacier is safer in that sense, as long as the hosting company doesn't go belly-up. Hard to see interfaces like USB, firewire, or SATA going away anytime soon, but still something you'll want to revisit every few years.
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