Tricky question, because if I mention one, the others are going to be upset and having at least 20+ 35mm lenses protesting can be a health hazard!
From a comfort point of view, I have to say either the 35/2 Summicron III or IV. They are small and easy to hold and operate and my fingers know exactly where the controls are.
For pure "image" quality it is a toss up between the 35f2 Asph (sharp and contrasty - a bit too contrasty in bright light) and the Biogon 35/2 ZM (smoothest tones of any 35 in black/white, more than sharp enough).
For convinience and small size, the VC 35f2.5 II and occasionally my old 35f2 I from 1958.
For all practical purposes, most of the modern lenses, particularly "prime" 35 rangefinder lenses are more than adequate for most every shooting situation, particularly if you are shooting black/white. I find that ergonomics of a lens is as important as performance. If the lens fits your hand and style of shooting, you are going to get better pictures than with a lens that is uncomfortable for you to use!
If you are looking for a classic package, a M2 and a Summicron 35, either version i (expensive collectible 8 element version) or the version III (less "collectible and thus cheaper) would be fine. The version IV and Asph f2 are too pricey for what they offer - at least in black and white. I much prefer spending less on the camera and lens initially and more on film. Once you are familiar with the camera, you will know what you need or want.
Lenses like the Konica/Minolta/Canon are other alternatives and they are all good - I particularly like the Canon 35f2 (or f1.8, virtually the same lens, just reduced in size for the f2 version). There are differences in rendition between all lenses, but not enough to disqualify any of them as useful 35's. In the end it is you as the photographer that determines the quality of the image, not the lens and the camera. My criteria is that the combination is going to perform for a long, long time and that I should never have to "think" about if it is "good enough".
I usually only blow prints up to 11x14 these days, but I have done 24x36" prints from old and rather scruffy 35f2's from the early 60's without much trouble. maybe a bit lower contrast and if shot wide open, slightly softer corners, but that is not whats important, it what is on the image that counts.
