I personally have used hotmail and gmail (google's email program). I enjoy google, and it's easy to use, even on mobile web (cell, pda/blackberry). Its completely free, and as of this moment, you get ~6.5 GB space (it's constantly going up), which is pretty massive. The chat function is pretty cool, and your chats get saved with your mail. As for the mail itself:

Instead of folders, gmail uses "Labels," which are added to a particular message. You can add more than 1 label to a message if you want, color code the labels (to make them easier to spot), and easily add or remove the labels.

Gmail uses google's search function to search your email, which for some reason doesn't appear to be as effective as regular google, which is the only flaw I've found with it, although most of the time it works.

Gmail's spam trap is usually pretty good at picking up spam without being too overreaching.

If you need an internet calendar, Google Calendar can email you your calendar and reminders daily, and also offers an "add this to your calendar" function, which can be found in emails with a meeting time and place listed.

Lastly, Gmail's conversation function makes your inbox a lot less cluttered. It groups together replies and messages from the same concept, into one heading in your inbox. For example, you get a confirmation from your airline. You forward it to me, I respond. This shows up as 1 conversation, taking up one line in your inbox.

Hope this helps