3 locations for SSHd configuration
If you look at the specific files you'll see that there are actually only two files (/etc/ssh/sshd_config and /private/etc/ssh/sshd_config is the same file unless your setup is non-standard).


/System/Library/LaunchDaemons/ssh.plist is used by the system to start sshd, usually you don't need to change this
/private/etc/ssh/sshd_config is the global configuration file for sshd, and the place where you need to change whatever is required to harden SSH on your Mac.