I have been very happy with mailbox.org. I recently signed up for early access to Thundermail, which is the new email service being rolled out by the Thunderbird team. I have no particular need to change except that I like the idea of supporting Thunderbird. So I will be keeping an eye on it.

If you use a custom domain and email clients rather than webmail, moving around becomes a lot easier. Another tip is to use a service like addy.io where you can create a new alias for every service, to help protect against spam.