What I don't like about GMail is the complete disregard for digital signing and encryption with S/MIME and/or OpenPGP.
Therefore, on my Android right now I'm using K-9 and on the desktop I use Thunderbird. Thunderbird is actually pretty cool once you customize it a little (it even works with Google's Calendar and Tasks). There's even a cool Chrome/Firefox extension called Mailvelope, for making PGP work in webmail interfaces [1] and so it works straight in GMail, though in Firefox, due to a current limitation that probably won't get fixed until 27, it's very slow and also the extension currently doesn't support PGP/Mime and can't sync with key servers, although the author told me these features are planed for the next versions. And since I'm a Firefox user, I'll just have to wait for now.
Note - I'm a Google Apps user, which means I have my own domain. I can always switch without losing my email address. If you're using a @gmail.com email address, then you should really stop doing that.