Depends what your needs are.
What are the Benefits of IMAP?
Since you can view just the header information without downloading the entire message, you can delete large messages without wasting time for downloading them. Also, because the messages remain on the server, you can access your mail from multiple locations at the same time and ensure that your messages are always available for you. And, since the messages remain on the server, if your computer crashes you don't have to worry about losing your messages. IMAP is generally faster and more reliable, especially with certain email clients such as Microsoft Outlook.
What are the Benefits of POP3?
Since all of your messages are downloaded immediately, after you check your mail at your computer, you do not need to actually be connected to the Internet to read your email. Also, because the messages are downloaded to your computer you do not need to worry about accruing disk usage charges because the messages do not stay on the servers. Just make sure your email client is set to delete email messages from the server after downloading them, or else all your emails will sit there, taking up space, until you use Webmail or an IMAP client to delete them!
http://faq.he.net/index.php/IMAP_vs_POP3