Which is better mbox- or Maildir-style mailboxes?
It depends on your situation. One critical point is that if your mail store is mounted over NFS, don’t use mbox. Otherwise, mbox is almost universally supported, but might be susceptible to file locking problems when multiple programs need access to the mail file. The maildir format eliminates file locking issues, but might not scale adequately on your system for users who keep very large numbers of messages on your server. As far as performance considerations, it depends again. With maildir, accessing a particular message and deleting is probably quicker, but with mbox appending new messages to the end of the mail file probably wins out. From the Postfix point-of-view, it doesn’t really matter. You can let other factors such as your choice of POP/IMAP server drive the decision. All else being equal, you should probably choose maildir.
