I have been using Yahoo for a long time now. The new Beta seems to be a big improvement on its current version. Of course, I am still waiting for a response from Yahoo on my offer to sign-up for the beta.
I have heard some good things about Google Mail, but just don’t have the patience to move to a completely different email address, and inform everyone of the change and what not –
Some links that showcase the new features –
Nice screenshots – http://patcavit.com/2005/09/14/y-mail-beta-impressions/