• SFTP is not actually an FTP solution.  It does not use the FTP protocol as the transport.  While named "SecureFTP" it actually is SSH based, an encrypted communication protocol. SFTP runs the communication over one port for both command and data (whereas FTP actually uses separate ports or sockets for command vs data).
• FTPS is FTP over SSL.  It is an FTP implementation which encrypts the communication sockets. Like standard FTP, it uses one port for command communication, and a different port for the actual transport of data.  It can be implemented in two different modes:
  • Explicit: This is the preferred method according to RFC 4217. The client connects to the server port 21 and starts an unencrypted FTP session as normal, but requests that TLS security be used and performs the appropriate handshake before sending any sensitive data. With explicit, you are able to specify if the data connection is encrypted or not.
  • Implicit:  the client connects to a different port (usually 990), and an SSL handshake is performed before any FTP commands are sent. With implicit, the data connection will automatically be encrypted.
• Though there is some varied opinion, it is generally accepted that these are comparable ways to securely transfer files.  

Related articles you may find helpful:

• Secure FTP (sFTP, FTPS) support on 3Essentials hosting
• Configuring your FTP client for FTPS