IMAP to POP. Why?
With POP3, mail is held at the server until the client greets it. At the time, the client downloads the messages from the server to the local computer and (usually) deletes it from the server. With POP3, there is only one folder on the server for each mail account -- the INBOX (technically, it's not really considered a folder, but that term will work for this discussion)
With IMAP, mail storage is at the server. The client may cache mail headers or portions of the mail body, but the server is the repository for the "real" messages. On an IMAP server, you can have several folders under your account. The beauty here is because IMAP is server-based, your email is identical everywhere you check it — work computer, home computer, laptop, smartphone, other computers, etc.