On Mac, I've always used the built in Mail client. But I just recently got MS Office for Mac which includes Outlook so I decided to give it a try. Not really sure which one I like better at this point.
mail.app Only problem is occasionally yahoo goes on the fritz and keeps popping up wanting the password re-entered. It's a third tier email for me that gets little use so not a big deal.
Outlook is a turd, I use Apple's Mail.
All mail apps on macs are shit. I hate using them on my Mac. I'd rather use the related web mail apps.
I just log onto gmail
Care to elaborate?
Mac mail is slow, horrible and error plagued with no clear error # indication. Entourage has to be the most bloated POS ever created. Outlook 2011 is better but it is still extremely slow and bloated and error prone without clear reasons why. This is all with Exchange email BTW. Pop3 or other emails are not as bad but in my experience most mac email clients are programmed rather poorly and regardless of computer horsepower they run extremely slow and god forbid you dont run the client for more than a couple of days, your email will be even slower.
I swear by Postbox:
http://www.postbox-inc.com/
I think it is cleaner / nicer than mail. Use it on both my PC + Macbook.
I can't stand using gmail on the web. It feels like every time I log in, they've jacked with the layout, or the buttons, or the colors, or who knows what. It gets irritating having to deal with their 'We made wonderful changes!' when all I want to do is just look something up real quick.