Gmail was built by engineers to manage email efficiently. Everything can be keyboard driven. Labels work better than folders. Filters super easy to create. I receive 200+ emails a day, and Gmail keyboard shortcuts are my go-to tool. Aside from sub-optimal (usually chorded) keyboard shortcuts, every local client I've ever tried has simply choked on the volume of mail I deal with, Gmail doesn't.
I use MailPlane to get the Gmail UI but with smooth integration into OS X and multiple Google accounts loaded in parallel with the Google multi-login nightmare.