I am in love with the Zeiss 21 mm f/2.8 ZE. Sharpness, color, microcontrast, even out to the edges.
I found a clean used copy of Zeiss 21 mm f/2.8 ZE at my local dealer for $1,200.00 . No lens hood, but I don't care about using aftermarket hoods and caps - in fact the OEM cap is not that great, I put a beefy Tamron 82mm pinch cap on it instead, and keep the dainty OEM cap for spare. The one bad thing about the lens is weight. My wide prime landscape lens kit weighs 3 kg (Samyang 14, Zeiss 21, Sigma 35 Art, AIS Nikkor 50 f/1.2 plus its adapter). Fine for hikes in the Ozarks, my home territory (well, St. Louis), with repetitive elevation changes of 100 to 300 feet, but if I ever got in shape for serious peak hiking in CO, I'd probably swap out the 14, 35, and 50 for a 40 f/2.8 STM and the Zeiss (or Scopar 20 f/3.5? I haven't seen this lens) and a pano kit for wide angle.