Do not ever use unencrypted protocols. Why should you?
There's no much overhead nowadays with current hardware.
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
Do not ever use unencrypted protocols. Why should you?
There's no much overhead nowadays with current hardware.
The only reason I have FTP at home in an old printer that only supports it for wireless scan uploads. Rsync with SSH is the best, learn what -a, --delete and --checksum arguments do - they are very powerful. To strictly answer the question - SFTP.
rsync over ssh is my preference, otherwise sftp. Don’t use ftp, everything over it is plaintext including your login credentials.
scp
Should I use FTP or SFTP when downloading files to a PC from a Seedbox?
What is safest when not using a VPN?
Do not use unencrypted connections. There is no reason to ever use an unencrypted connection. FTP is obsolete, it was used in a time when encrypting and decrypting data was too resource intensive for the processors available.
That time has long since passed. People have been born, have grown into adults and have had children of their own since then.
Don't use ftp, don't use http.
Use SFTP or FTPS, plain FTP should not be used.