Use POP3 for viewing AND archiving your email. Use IMAP for viewing your email. IMAP keeps your email on the server (for a certain period of time). This is useful for mobile devices because it doesn't bog up your phone memory. POP3 downloads the email to the local device. This is useful for a PC where you can keep a running backup of all the email that have hit the server. 

If you plan to use multiple devices, we recommend you setup a PC (with Outlook if you have it) for your POP3 account and in the settings set it to leave a copy of the email on the server for a week or so. Then your mobile devices will have access to your current emails.