I was a huge fan of Sparrow before Google acquired it last summer. It was a fast, beautiful email client for Mac and iPhone, and I was heartbroken when the team announced that it wouldn't be receiving future updates. Apple's native Mail.app is acceptable but not wonderful, and alternatives like Postbox tend to focus on adding features for power users, rather than making email easier.
I hadn't been following development on Airmail, but after a few days with it, I'm please to report that it's everything I had hoped Sparrow could become. It's super-fast, looks great, supports a huge range of account types, and successfully balances a large set of features with a great user experience. If you're a Gmail fan looking for a native app, you'll find yourself right at home.
I'm really excited to see how Airmail develops over the coming months, and hope that it makes its way over to iOS sometime in the near future. It's only $1.99 on the Mac App Store, and I highly recommend you check it out.