I've used Rsync before, but as of now I am using cPanel backup option only. But one think I can surely tell you; Rsync can help to reduce on transfer size, but if that is not an issue, so there is no sense in switching. In my opinion, R1Soft is much better option than rest of other two.
Generally, I use cPanel backups for my various sites. I've never had a single problem with it. But I could see the bandwidth being a real problem. So if you have a large sites, then you have to consider Rsync or R1Soft. But if you have a small wordpress sites, then you should also check the wp exports option. It is a solid way to back up your content.
For few websites, cPanel backup option is fine, but for large sites; it is not that much good, but this is just form my personal point view. However, as per the web host's point view, definitely you have to consider Rsync or R1Soft solution.
R1Soft is the most advanced backup application available at the moment and hence my vote goes to it. It offers backup solution for managed as well as unmanaged hosting packages as well as backups for virtualization machines (new).