For winbox’s there are two standard choices:
PPTP and L2TP
Depending on what you are trying to do, you would choose the appropriate one.
PPTP port 1723 TCP or PPTP port 1723 UDP
L2TP port 1701 TCP or L2TP port 1701 UDP
Each one of these provides a different level of authentication, security and encryption.
You can safely rule out the UDP options here, because you probably want a true tunnel (end to end).
Now the big question is how secure you want to be??