scp: fast, straightforward, speed shown by default.
rsync: good for avoiding duplicate file transfer, or in other words, transferring files on-the-go.
-z: compress/uncompress file data before/after transferring.
-a: archive mode, which allows copying files recursively and it also preserves symbolic links, file permissions, user & group ownerships, and timestamps. This is important when you try to synchronize the data, as timestamp difference is also taken into account.
rclone: good for cloud service, or transfer data between storage and compute nodes.