Hard Disk – When used on a regular basis a hard disk will typically last for around 5 years 

Optical – Standard optical media includes CD, DVD and BluRay, last half that time before the aluminium starts separating from the plastic.

Flash Media – Clearly you would expect that since Flash Media has no moving parts it would be ideal for a long term backup strategy.  To an extent you would be right but the published data retention of a unused flash drive is only around 10 years

Tape – This may come as a surprise, but Tape backup actually holds one of the best data retention rates hence its continued use in banking and government sectors.  Typically a manufacturer will warranty a tape for 30 years