I work with VMs mostly, so I go for Veeam B&R. The free tier allows you to backup 10 VMs or machines.
Free and Open Source Software
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I've used borg for a while and like it a lot. I would say your best option for pure linux is borg+borgmatic/vorta just because borg is battle-tested.
If you run any other OSs and don't mind a relative newcomer, I've found kopia to be easy to recommend to my windows friends. At this point kopia has been around long enough (~4 years of actual beta) that I think it's safe to trust its integrity with personal data. It has all the important features from borg in a cross-platform solution, so it's also a viable alternative for borg on linux if you don't like borg's frontends for whatever reason.
ZFS snapshots and Borg(matic).
I use FreeFileSync. It's the only GUI tool I found that let's me sync folders while omitting file deletions. It lets you create batch files from the GUI that I execute with crontab multiple times per day.