Rather than attempting to rate the programs, the main intention here is to help you find the program that best meets your needs. The reason for this approach is simple. It's impossible to pick a single email program that fits all people. That's because we each approach the world of email in different ways.
Some people check their mail only occasionally.
Others have their email software set to check their server or servers every few minutes. Some like to read through all the new mail, delete most of it, and then file away the rest. Others want their mail to be presorted for them, and view it by categories, preferably in discussion thread order in the case of mailing lists. The kinds of mail people receive also vary widely. Some people belong to a number of different mailing lists, so they usually want to keep mail from each list separate.