Bupstash (https://bupstash.io/) beats Borg and Kopia in my tests (see https://masysma.net/37/backup_tests_borg_bupstash_kopia.xhtm...). It is a modern take very close to what Borg offers regarding the feature set but has a significantly better performance (in terms of resource use for running tasks, the backups were slightly larger than Borg's in my tests).