Myself I have all but given up on GUI email clients, I still use Thunderbird from time to time but only when I need PGP encrypted email, otherwise I stick to webmail. I am looking forward to Mailpile if it delivers on its goals, looks very promising.
http://www.indiegogo.com/projects/mailpile-taking-e-mail-bac...
To me, Thunderbird + Nostalgy + Enigmail + Colored Diffs = bliss.
I've recently been trying trojita as my imap client (have been using mutt otherwis). It's fairly feature simple, but blazingly fast.
I'll poke at Trojita but it'll have the same confidence issue by virtue of being relatively new.
3.0 was a radical departure from and regression in speed, stability, and usability relative to the 1.x and 2.x series.