The only problem with tapes is that they are magnetic media. Magnetic media does fail over time. I'd say CDs are your best bet for long term.

As far as Iomega disks (Zip and Jaz)--I've found the Zips at least to only be as reliable as the drive they are used with. The USB ZIp drive in particular seems to eat Zip disks although I never had a problem with Zips in an internal drive that was in a Dell I used to own. I have used the SCSI Zip drive but not enough to make a good judgement call. I've never tried a Jaz drive but I'd imagine the drive quality issue exists there too (it seems as though the components were cheapened as the technology aged, sort of like what we've seen with floppy drives).