imap server and security

Hi, i am planning to build a mail server for 30 users with suse linux but i don't kown what imap server to use ( cyrus - courier - dovecot - etc.. ). I read that dovecot is the better choise for security. My users must manage large mailbox ( from 100M to 1G ) but in this case i read that is cyrus the correct choise. What do you think? Best regards, Cristian Del Carlo