The schneider Xenar 135 has a nice rendering for out of focus areas and may be a bit soft in the corners if shooting f8 and below. At f22 the corners are sharp and the flare is minimal. The Nikon 135 is a bit sharper overall and has increased local contrast due to multi-coating. The newer the lens the more reliable the shutter is likely to be.

I never liked the 150mm for unknown reasons. Probably for the same reason I prefer the Minolta 45mm vs 50mm on most 135 cameras. Or the 40mm voightlander lens on my M3.