Seaweedfs is more mature and has many interfaces (S3, webdav, SFTP, REST, fuse mount). It's most appropriate for storing lots of small files.
I prefer the command line interface and data/synchronization model of Garage, though. It's easier to manage, probably because the developers aren't biting off more than they can chew.
Like in the old MinIO days, an S3 object is a file on the filesystem, not some replicated blocks. You could always rebuild the full object store content with a few rsync. I appreciate the simplicity.
My main concern was that you couldn't configure it easily through files, you had to use CLI, which wasn't very convenient. I hope this has changed.
Configuration is still through the CLI, though it's fairly simple. If your usecase is similar to the way that the Deuxfleurs organization uses it -- several heterogeneous, geographically distributed nodes that are more or less set-it-and-forget-it -- then it's probably a good fit.
My use case is relatively common : I want small S3 compatible object stores that can be deployed in Kubernetes without manual intervention. The CLI part was a bit in the way last time, this could have been automated but it wasn't straightforward.