FTPS is FTP with SSL for security. It uses a control channel and opens new connections for the data transfer. As it uses SSL , it requires a certificate.
SFTP (SSH File Transfer Protocol / Secure File Transfer Protocol) was designed as an extension of SSH to provide file transfer capability, so it usually uses only the SSH port for both data and control.
In most SSH server installations you will have SFTP support, but FTPS would need an additional configuration of a supported FTP server.