Gmail for me.. can't go wrong with an app that's been out for quite a lot longer than inbox. Also, I'm a simple man with my email. Exchange support on Nexus devices is a plus too. :)
I too have higher than usual android os usage. Doze seems to be working fine for me though. Just don't know what can be keeping my phone awake. I do not use any social apps. Wondering if the 5ghz wifi is a cause. Will test that out.
Nexus 5X for me please. After owning the original nexus 5, a phone that defined low cost and awesome specs, the 5X is following in its footsteps and doing a great job at it. That minty color though... ;)