Which of the following is the BEST protocol to use for securely transferring large files?

Telnet transmits all data including usernames, passwords, and file contents in clear text, making it completely unsuitable for any secure operation.

SSH provides a secure encrypted shell for remote command execution but is not itself a file transfer protocol - SFTP is the file transfer subsystem that runs over SSH.

SFTP (SSH File Transfer Protocol) runs as a subsystem of SSH and encrypts the entire session including credentials and file data using SSH's encryption (typically AES). It is purpose-built for secure file transfer, supporting large files, resume capability, and directory operations, while providing the strong authentication mechanisms of SSH.

FTP (File Transfer Protocol) transmits credentials and file data in clear text on ports 20 and 21, with no native encryption, making it insecure for sensitive file transfers.