I mainly use webmail. But when I need a mail client, it is "nmh" for text mode (command line), and claws-mail if I need a GUI.
I also have Thunderbird and kmail installed. The last time I tried kmail was probably around 2000 - I guess I should give it another try. I'm surprised that you don't have evolution in your poll.
On claws-mail - it is simple, but adequate, it integrates well with "nmh", and it is available for Windows.
More general comment: I prefer that mail be not too tightly integrated with the desktop. When I install an new version of linux, I like to delete all of the prior desktop configuration and make a fresh start. But that would risk losing email with a client (evolution or kmail) that is too tightly integrated.