[Dovecot] Best authentication option

[Eric]

Dear Dovecot experts,
I have a small home server debian based, with postfix/dovecot/squirrelmail
installed locally and working. Dovecot is used non-secured (no imaps) but
only on the 192.168.0.100 address (address of the server on the local
network). I want to use squirrelmail to read my email from outside.
Squirrelmail can configured to access it in particular, either through
cram-md5 or login auths.
In that situation, is it better (I mean more secure) to use : 1) auth
mechanim = cram-md5 or 2) auth mechanism = plain (using PAM authentication
for dovecot) ? That will determine my dovecot configuration.

Thank you

Eric