This mail seems to be mixing up mail clients and mail providers.
Mail Providers
Yahoo's new RocketMail service isn't bad either, if you like web mail interfaces. It's not a mail client, but a mail provider.
I haven't tried them yet, but I have a few friends that really like GMX (
http://www.gmx.com) as a mail provider.
Mail Clients
I too use Thunderbird. I recently upgraded to Thunderbird 3, which is now out of beta. I really like it. The new style search drives me nuts, but is is very easy to disable and go back to Thunderbird 2 "quick search" mode.
I think ideally, you'd use Gmail as your provider, to do things like spam filter, and then use an IMAP connection through Thunderbird to it if you want a desktop client (perhaps for managing multiple accounts.