I use two email clients regularly – one for my normal email accounts, and one for my work email because it goes through SSH port forwarding and receives tons of messages. It is a pain to have the two email setups set up in the same email client.
I use Mac OS X machines at home, and I really like Apple’s Mail.app. I use it for my normal email accounts. The UI is superb, it’s fast, stable, and has excellent junk mail filtering.
For accessing my work email account from home on Mac OS X, I have been using Thunderbird. I use Thunderbird extensively at work on Linux and it works great. However, using Thunderbird at home on Mac OS X has been surprisingly displeasing. The UI is somewhat flakey and unpolished, it’s slow, and it doesn’t look or behave in a convincinly native way. Most irritatingly, keyboard navigation of email lists is really quirky – sometimes hitting buttons doesn’t work and using key modifiers doesn’t have dependable results. Also, the UI doesn’t always update correctly – sometimes I select an email and the display pane just goes blank or stays on the previously selected email. Because of this, I have switched to using Microsoft Office’s Entourage email client for accessing my work email from home. I almost hate to say it, but its been a very pleasant switching experience. MS did a pretty good job on Entourage (though it’s no Mail.app).
Thunderbird on Linux and (from what I hear) Windows rocks, but it really needs some work on Mac OS X. I’d love to fix my problems with Thunderbird on Mac OS X, but I just don’t have the time. There is a lot of potential there though, and I have no doubt it will be realized sooner or later.