In the film era to which these lenses are native, I'd rather have the imagery from the Summicron on my film, particularly color reversal. However, the Nikon lenses focused closer and cost 1/4 as much. In the digital era, the Leica lenses might not be able to be fairly compared, due to the vagaries of steep ray angles vs. digital sensor sensitivity to same. SLR-intended lenses tend to fare better on digital sensors.
EDIT: I realize you didn't specify whether Leica M or Leica R. I assumed M.