CD or DVD
I recommend CDs or DVDs. Use name-brand. And before you start, research CD and DVD life-spans on Google.
Disk drives don't last more than 5 years or so (according to posts on this site), and magnetic tape will go bad sitting in the box.
If you insist on using hard drives, make multiple copies (as susggested elsewhere) and make dupes onto half-way new HDs every year or two.
BTW. When making backups, put a copy in a place outside the home, incase of fire or burglary.