I'm running the Nexus 6P, on google fi, and it's the best phone I've ever used without question. It just works perfectly all the time, and its camera is quite nice.
Its mic and speakers are extremely good, too, and that's enabled a new usage of the phone compared to prior ones.
You can set up google now to work and unlock your phone when locked, and it does so by recognizing your specific voice... so if you say "Ok Google" it'll unlock your phone and do whatever you want... but if someone else does, it ignores it. Although apparently my voice sounds like Jake Gyllenhaal, and I was watching "Enemy" last week and at one point in the movie he says some like that Google thought was me saying "Ok Google" which was weird.
Anyway, due to the mic and speakers being so good, I can use google now to do stuff without taking my phone out of my pocket at all. I can just say, "OK Google" and then ask it whatever.. turn on my lights, check the weather, whatever. And it operates perfectly well from within my pocket, and the speakers are loud and clear enough that I can hear its response clearly.
I have no idea if anyone other than me would ever use it like this, but I like it.
Oh, also, the fingerprint reader is good, and I really didn't expect to care about it at all, but having it automatically unlock my phone when I pick it up is slick.
And god damn if it isn't nice to have a nexus phone... vanilla android is just so clean and nice.