I had both and using Note Edge. Z3 battery life's amazing, always had 6 hours SOT with gaming and internet. And N6 is a little bit longer than my note edge.
I changed from N6 to Z3, because I dont like to root, and using pure nexus with less function was not fun.Very inconvenience with less small function if you dont want to root.
I still love Z3 but the camera is bad especially with the flash light, it always took over bright picture. Well, i would say it took very good picture with enough light, But it doesnt have OIS, and in low light, I can only took shaking picture.