Edit 1: Life Itself has crept into the top 10. After Tiller drops down.
It's honestly a toss up between 1-3 on this list. On any given day I could probably say any of them are my #1.
I was not able to catch CitizenFour yet and am anxious to see if it makes the cut. I also missed Rich Hill, Happy Valley, and The Grim Sleeper (amongst many more I am sure).
Honorables: Last Days in Vietnam, The Battered Bastards of Baseball, The Unknown Known, Jodorowsky's Dune, Art & Craft, To Be Takei, and The Armstrong Lie.
I don't usually do a bottom 5 for Docs but I would like to mention that Fracknation is horrible. On every level.
Most disappointing doc: The Unbelievers. While not strictly speaking a bad film it does feel extremely unecessary and almost plays like a weird ego stroke to Richard Dawkins.