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In choosing the right FTP, the answer would depend on your goals and requirements. Generally speaking, SFTP is superior to FTPS. It would be a good idea to implement both protocols; however, they are different in terms of their concepts and supported commands.
If you have a server that have FTP support but does not have SFTP/SSH clients or it needs to be accessed from personal devices such as PDAs, smartphones, etc), it is a good idea to use FTPS. However, if you are building a custom security solution, the better option is SFTP. As for the side of the clients, the requirements depend on the server that you plan to connect to.