Short answer: POP3, because it works best for normal mail users in a home or office situation where you have a single PC that handles all the mail. It also causes less problems with server mailboxes filling up and causing mail delivery issues

Long answer: It depends on what you want to use it for but then you also need to understand the issues that comes with using IMAP

First of all you need to understand the difference between POP3 and IMAP. POP3 downloads the full mail message from the server to your PC and IMAP only downloads the headers (From, Title, etc) and shows these to you and if you select a message it will download the message body as well so you can see the content, leaving the mail message on the server

POP3 is used to download all mail from your mailbox on the server to your mail application on your PC. If your mail application is set to remove copies of the mail from the server, then all mail will be removed from the server mailbox when it is downloaded, cleaning out the server mailbox so more mail can arrive. If the mail application is set to leave a copy of the mail on the server, then the mail will be downloaded to your PC but a copy will be left in the mailbox which then can be accessed using the Webmail interface or possibly using your Mobile device. However, leaving the mail on the server may cause problems with a full mailbox which will stop all mail delivery to the mailbox so you will have to be careful how you control it - either allocate sufficient space to the mailbox or set your mail application to rather delete the mail once it's been downloaded

IMAP is used typically in a situation where you want to access your mail from multiple locations and one multiple devices, and so you do not download the mail to one device only but rather leave it on a central server which can be accessed from anywhere you have an internet connection. This is similar to the way Gmail and Yahoo mail works. However, on a hosting account you typically only have so much space available, so uncontrolled IMAP use will use up your server space quickly and cause mail delivery problems due to full mailboxes