I like Thunderbird, but on Linux I finally switched to Evolution because Thunderbird was an absolute RAM and CPU hog, and also, Google Calendar integration was flakey as hell. Thunderbird would randomly decide to not notify me of an event or decide to notify me way too late.
I would use Evolution if it didn't look and feel like the version found in early GNOME 2 Ubuntu, when they still used to ship installation CDs for free.
Aesthetics is as important a feature as supporting IMAP or having decent search. Which is why I'm still stuck with Fastmail's webmail, because neither Evolution nor Thunderbird seem to satisfy these criteria.
