I have been kicking around the idea of ditching my mail client ever since Sparrow was bought out by Google. I discovered PostBox which worked great for a while but seemed to be bloated and slow after using it for a while. I then came across AirMail which is a great replacement for Sparrow but recent updates seemed to have slowed it down, and also based on some of the open discussion about where its going it sounds like it also is going to get bloated and eventually be a slow client. Maybe once things are a little more set in stone and its not so Beta I might have to look at it again.
A while back I was in the market for a new email client as I was not really excited with the functionality of Mail.app. I ended up deciding to use Sparrow, after using it for about a week I was sold on it and couldn’t imagine using any other mail client.