I use Apple Mail on my MacBook Pro, mainly because it has a better integration with Spotlight than Thunderbird. It also has a nicer UI and is easier to configure.
However, the keyboard shortcuts are really strange. In case you didn’t find out yourself, here are the most important ones:
Send message – CMD+SHIFT+D (what does the D stand for? Deliver?)
Apply rules to selected mails – CMD+ALT+L (L for ruLe ???)
Select all messages in a thread – CMD+SHIFT+K (K for seleKt ???)
Erase junk mail – CMD+ALT+J (now, this is obvious – J for Junk)
Apple developers, if you read this, please comment on the deeper meaning behind the shortcuts.