E-Mail Client Recomendation

Now that Gmail uses IMAP I'm interested in using an e-mail client application. I know how to setup them properly. However, I haven't used them intensively.

So it's just for basic stuff, just read and send e-mail. I have Office 2007, but the Outlook thing seems very big a complex to me, so it will use more memory. There's Windows Live Mail, the successor of Windows Mail and Outlook Express, but it's a MS offering and there always people unhappy with MS things sometimes (I use Windows, and Office, but I use Firefox for example). And finnaly (speak of the devil) there's Thunderbird, Mozilla's offering.

I just really do basic stuff, and I need a fast, secure and robust thing. What do you guys recommend?

Tested Windows Live Mail, and gave issues with the IMAP service sometimes. Tested Thunderbird and works flawleslly... Dunno about Outlook 2007 yet... BTW Is there a way to easyly get all the contacts from gmail exported to Thunderbid?

Alright, Thunderbird here, thanks everybody