...not sure a hard drive will last 50 to 100 years without bearings or something similiar siezing up. BOTH methods also assume we will have an operating system (Windows 2100?) that will still read either device!
Of course data CAN be retrieved from a hard drive even if the drive has been under water and often even in a fire. The data recovery is expensive however. Are the 'platers' that store the data on a hard drive more secure than a DVD locked away from sunlight, seldom or never played? Will anyone CARE 100 years from now?
Hmmmmm....