MarkPS

The answer depends on what you want to shoot.  I do a lot of street photography. I use a 35mm summicron on a Leica M10R.  I did find that the 35mm was a little short for some scenes in Miami and I had to crop the frames a lot.  I also have a Leica 90mm, which I found is a little difficult to use in the  street due to the tight image and small frame lines in the viewfinder. I recently bought a 50mm Voightlander f2 APO Lanthar, which is a fantastic lens and costs 10x less than a Leica 50mm AP0. I switch off between the 35 and 50 but, candidly, to my surprise, I am enjoying  the 50mm focal length. There is no correct answer.  If I had to pick only one lens for street photography it would be the 35mm lens.  If you want to shoot tighter images or some head and shoulders portraits then a 50mm is great.  BTW, you can pick up a used 50mm Voightlander Lanthar for under $900.  Another choice that you might consider is a 75mm lens.  A 35, 75 combination might be what you would like.  Again, if you want the 75, my choice would be either the Voightlander Nocton f1.5 or the newer Voightlander Ultron f1.9.. For now I am sticking to the 35, 50 and 90 combination that I own.  Best of luck in your choices but you can’t go wrong. 

The M11 has a difference in weight between the silver and black editions. The silver is heavier and made if a different material.  The M6s weigh the same regardless of color.