Storage backends… this one is tricky and I am not sure myself what is the best way to compare it.
Let’s say S3 - both restic and rustic support it out of the box. “via opendal” for rustic suggests that some extra software is needed which is not true. It is just technical implementation detail. restic I bet is using some 3rd party library here as well.
rustic supports much more backends without need to install and configure additional software. But both support rclone for whatever this handy utility supports.
From end user perspective this is what I am interested about - what I can use for repo without anything extra. And with rustic for example I can use onedrive when with restic I would have to install and configure rclone