It's never easy comparing lenses with different focal length and aperture, at least they have similar entrance pupil wide open so that equalises things a bit. Framing the subject similarly (by changing the distance for each lens) seems like a sensible approach in this case.
In terms of colour, the Zeiss looks a little cleaner, brighter. The Nikon looks slightly more muted and mellow. This could be due to the different cameras, so cannot come to any firm conclusions here.
In terms of bokeh, the Nikon looks a little smoother, rounder, in spite of its shorter focal length. The Zeiss is good but the backgrounds have a slightly more textured appearance.
The close focus ability of the Zeiss is impressive and a point in its favour.
On the basis of this comparison, the Zeiss lives up to its reputation for a very clean "clinical" rendition. The Nikon is a smoother, a bit more character. For portraiture I'd choose the Nikon. For landscape and closeups, I'd go with Zeiss. Actually I go with neither, can't afford this type of glass!
