This depends on how many different computers or devices you want to view your e-mail from.
If you are simply wanting to collect mail from your account to your e-mail program on a single computer, POP is best for this – it downloads the mails to your computer then removes them from the server. (You can normally also select to leave them on the server for a certain amount of time, allowing you also to download them to a second computer).
IMAP allows you to view what mails are in your mailbox on the server, and it leaves them there. This requires an Internet connection – i.e. when you disconnect from the Internet you can no longer see your mailbox. This method is best if you do not want to be tied to a particular computer, or if you are using a mobile phone but want to leave your mail where it is and collect it from a computer later.
Posted in: Questions concerning e-mail