what does mail have that outlook or thunderbird don't have? outlook 2010 and thunderbird 5 are quite good i think.
Also, i am loving the new conversation view add-on for thunderbird!
Like I had said, Outlook is closest, Mail is simpler than Outlook, which is both a pro and a con, but they are both fairly fast and responsive. I ran an experiment about a year ago where I tried basically every desktop email client that had a decent number of users, and none of them were good. The great things about Mail, at least for me, are;
1: It is fast. Switching between messages, folders, and deleting messages is all almost instantaneous, and that was pre-SSD. On my Air, it is amazing.
2: It is free (in this case built into the OS, but same difference)
3: Type in your gmail user/pass, it is configured.
I cannot recall if I ever tried Thunderbolt 5. I tried Thunderbolt, but I cannot remember what version it was.