Hard to say as I do not use any of these. One would have to have time to try them which I do not have.
Some ideas:
-Backup in a non-proprietary format
-Backup both bare metal images and at the file level.
-Ability to mount the backup to recover even a single file.
-For Windows Linux Mac
-Easy centralized multiclient web interface.
-Allowing backup to various cloud platforms as well as locally.
-Auto verification of backup validity.
-Ability in case of disaster to start the backup on virtual machine.
At a quick glance it seems to me that Bacula and Kopi are the most interesting.