The Sigma is better for your purposes although the Nikon is optically the better lens. The Sigma has more pleasant out-of-focus characteristics (aka Bokeh) and, on top of that, a much better focus ring (long throw, good grip) for video. The 2/3 stop extra aperture is nice but not so important.

See also this:

I like the Nikon f1.8G, I use it with a Novaflex adapter (with stopless aperture control. Aperture control is needed on any adapter). It's really lightweight (plastic) which is a bonus I think. The bokeh wide open looks a bit choppy, and as you close it down a stop it ceases to be an issue. But as the video says it's sharp.

Its funny, I have photos I took with that lens in the same place as in the video, Tai O village.

Nikon’s 35mm f1.8 G ED is a lens that won’t excite those us that always reach for higher hanging fruit, but it will surely satisfy the appetites of those that are looking for a fairly affordable 35mm prime lens. Best of all, this lens is designed for full frame cameras as opposed to the last one which was for APS-C DSLRs.

http://www.thephoblographer.com/2014/06/26/review-nikon-35mm-f1-8-g-ed/