A bug in Thunderbird made me switch to Evolution, recently. Every time it connects to my mailserver (right before STARTTLS) it just crashes:
[alex@thor ~]$ thunderbird (process:3124): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed enigmail.js: Registered components mimeVerify.jsm: module initialized Segmentation fault (core dumped)
This happens with a newly created, clean profile as well as with my long-used one. I haven't found the time to dig into - if I find out something I'll report it upstream.
For now, lack of time, I'm quite happy with Evolution as I have all the PIM stuff ready without a single plugin, and application performance is quite impressive compared to Thunderbird (looking at you, XUL...).