If there's one single reason to use an Android device, Gmail may be it. What once was the world's longest beta test is undoubtedly (though we may be a little biased here) the best way to manage email. It's available anywhere, at any time. It makes it virtually impossible to accidentally lose mail. Plus it's as fast on mobile as it is on a powerful desktop computer.
Gmail does things a little differently, keeping your conversations as, well, threaded conversations — not just back-and-forth messages like back in the Dark Ages. It's a different way of doing things, but it works. And it works well.
If you haven't yet tried Gmail, you're absolutely missing out. Gmail comes standard with a Google account, and with it you'll get multiple gigabytes of free storage, so you shouldn't be running out of storage space any time soon.
The Android app continues to improve as well. It'll be refreshed with Google's new Material Design language. And it'll continue to lead the way for all other mobile email clients — especially on Android.