The most valuable part of a data backup system is its file integrity. If something does not work properly, it only takes one problem to mess it all up.
Current industry leaders in online data backup systems such as Mozy.com and Carbonite or Ironmountain.com ALL do not guarantee restores. These companies are not setting the standard although they may be popular at the moment.
With tape backups there are no guarantees. Tape is fault prone and becomming quickly an out-dated backup solution. Read this pdf article on the problems with tape backups.
Having a Guarantee with a cloud hosted backup solution is the best data backup system. It is the best for individuals and companies alike.