I still think the HTC One M8 GPE version, once it gets 5.0 Lollipop officially next week, IMO is the best stock Android phone to date. Mainly because it's a one hander, with a manigable screen size, and not some freakishly huge 6" display. The Nexus 6 is also a very wide phone, pretty thick, and heavy. Just no way can it be used one handed.
Or even the OnePlus One, when CM12S is out. Plus the battery life on the OnePlus One is off the charts wickedly great
I think 5.5" screen size is the biggest that can still be a one handed phone, especially if done right like the LG G3, they built a 5.5" device so minimal in size, it feels much smaller. I wish Google would have made the Nexus 6 a 5.5" screen and based off the LG G3, just with the newer hardware inside.
Or Google should just make every flagship phone have a GPE version, then we could choose which specific device we want. Maybe a Galaxy S5 GPE people might want, or a LG G3 GPE. Give us that option at least.