Get the Zeiss ZM 35mm f/1.4 Distagon in silver or black ($250 rebate at time of post). See also my Leica M wish list and Leica SL wish list.
In Guide to Leica are two pieces, one lens-oriented, the other on the ugly digital artifacts that result from using a relatively low-resolution 24MP sensor without an anti-aliasing filter:
Aperture Series: Cerro Gordo Miner’s Coveralls (Leica SL)
Leica SL: Color Moiré Example
Includes images up to full 24MP resolution, at f/1.4, f/2, f/2.8.
f2 @ 4.0 sec, ISO 100; 2016-06-09 20:06:19[low-res image for bot]
LEICA SL (Typ 601) + Zeiss ZM 35mm f/1.4 Distagon