Not the previous poster, and I don't use Kopia, but after reading Kopia features and docs, they seem to be in par. I use Duplicati quite extensively for personal backups, and didn't really have any issues.

Duplicati has a web interface, so with a proper authentication in place, you can use it to remotely monitor and manage backups.

Duplicati doesn't keep a local cache. It uses SQLite files for file meta data, but not for the content themselves.

I like Duplicati's snapshotting mechanism. You can specify how long or how many snapshots to keep, and my anecdotal evidence is that it's archival storage-friendly. I imagine S3 and it's lifetime management rules can bring a decent and cost effective backup solution.

I'm using Google Drive 2TB plan, and I didn't see Kopia supporting Google drive out of the box.