I've been really happy with the Supcase Unicorn Beetle. It's like a hard bumper case that protects the back and sides (front is exposed).
https://smile.amazon.com/gp/product/B015X90UJS/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1
The Diztronic case was the first one I got since I liked it for my OPO, but I eventually bought the Supcase Slim instead http://www.amazon.com/SUPCASE-Release-Unicorn-Premium-Protective/dp/B015X90UJS/
The Diztronic's buttons popped out too much so I tended to hit them when picking up the phone and when I had the phone lying on its side when using it in bed. The Supcase buttons take a bit more pressure to click which helped with both problems above.
I would highly recommend the i-Blason UB PremiumSlim Hybrid case. It think and low profile. https://www.amazon.com/SUPCASE-Release-Unicorn-PremiumSlim-Protective/dp/B015X90UJS/ref=sr_1_1?s=wireless&ie=UTF8&qid=1486738310&sr=1-1&keywords=nexus+6p+case+supcase
I bought a set of znaps for USB-C, and this case http://www.amazon.com/gp/product/B015X90UJS?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
This tempered glass screen protector and this case. $17 shipped from Amazon. Now I just need my Storm Trooper to show up and slap them on him :).
This is the one I use, and I think it's pretty decent: https://www.amazon.com/gp/product/B015X90UJS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Though now I might give that leather one a try for a bit...
SUPCASE Unicorn Beetle Series for Nexus 6P - hands down. Fits snuggly and is sturdy enough to take a fall. Not sure if this is as low profile enough for you. It's very thin and has groves on the side to help with grip. In addition, the four corners are slightly raised so that it won't slip out of your hand. No cutout for the buttons though. I got a clear back so I can see the word Nexus but there is a pure black option. Simple, solid, and as a nice touch, the company's name is on the back and is small. Let me know if you have any questions. I can provide a picture of what it looks like with the case on if you'd like.
Amazon link
I have this case, I use it with a dbrand skin, and a screen protector and it works pretty decent, not overly bulky and helps prevent bend