Borg supports local and SFTP backups while Restic supports more (a lot more). S3, Google Cloud, B2, etc. In fact, they integrate with rclone so anything you can access using rclone, you can backup to using Restic.
Borg uses compression while Restic does not. Restic just uses deduplication so your backups with Restic will likely be larger in size.
Anyway, that's what jumps to mind. They're both pretty great honestly (in terms of community support and reliability). There are a lot of other options too btw. The Restic repo has a pretty good list [1]