The question don't exist. The Medium Format frame is absolutely better, not only in respect to the Leica M or Zeiss Ikon ZM cameras, but in respect to the all 35 mm cameras. In 1930, when was born the Leica II, there are the Zeiss Ikon Super Ikonta or Voigtlander Bessa models, in 4,5x6, 6x6 and 6x9 frame. Why the Leica concept was winner? For compactness and lightness, large selections of formidable lenses, more numbers of shots: all true winning cards in the photojournalist play. In the architectural or landscape shots, the bigger dimensions of the medium format films make the difference.
For the same reasons, the Nikon F and the others professional SLR 35 mm have won the medium format SLR Hasselblads and Rolleis: moreover, a shot of a Planar 80 surely won a shot of a Nikkor 50, in therms of pure image quality. In this case also, the choice between the 35 mm or medium format is simply the job: street photography on 35 mm, landscape or architectural work in medium format.
Naturally, the street photography is very superb also with the Mamiya 6 or 7, but whit only 12 or 10 shots, while the Leica M7 or the Zeiss Ikon ZM allow 36 shots.
Ciao.
