Sometimes there is the confusion between the two secure file sharing protocols.
They do similar things, and if you are hosting a website the hoster most likely provides both protocols.
But for there is a fundamental difference between the two.
FTPS was created as an afterthought for the older File Transfer Protocol (FTP) which dates back to the 1970s.
Some would say it was an easier time, no need for encryption, and clear text authentication was the norm.
But as we all know the landscape of the internet changed, and the need of a more secure version arose.
So in the 1990s FTPS was first specified. It utilised the newly born techonlgy of SSL to secure the old protocol.
SFTP on the other hand, is a much newer protocol and is based on the Secure Shell Protocol (SSH).
SSH was first defined in the mid-1990s as an option to securly remote into a remote system.