Confused on which would be a better method

I have Duplicati running on a Linux Box (Fedora) it is running as my name rather than root.

I want to be able to backup several other Linux and Windows Systems to my Backup Server.

Question: What is the best way to have the client machines see the backup storage? By mounting it as an SMB share, using SFTP, ?

Windows has some quirks using network shares, where the current user is used to authenticate against the share. This causes problems when you do not have the SMB config and the user config in sync.

If you want to allow the machines to make backups outside your current network (or prefer a Zero-trust network) the SFTP protocol is designed to be deployed with hardened security, accepting only keys and no passwords.

The setup with pub/priv keys is more work, but much more secure.

An alternative is to use something like MinIO on the storage machine and then having the clients back up with S3 and account keys.