[Dovecot] Best Imap Transfer Tool?

So I'm looking to do a migration of my IMAP mailboxes, and I'm looking for the best tool to use. I used to use the uw-mailutil tool, a while ago, but that was a bit coarse of a tool. More recently I've used imapsync, but that was giving me some errors. I've sort of tracked those down; but I was wondering if anyone else had any other recommendations...?

Thanks.