I agree with Greg.
My choice is a 1953 J-3 re-lubed and shimmied for Leica-M, then close-focus modified. This is a fantastic all-rounder regardless of the price.
It's fast. It's very lightweight. It looks like a cheap old lens, and nobody objects to having their photo taken with it. It's almost like they look at the age of the lens and subconciously understand that every facial blemish will not be recorded in exacting detail.
At 1.5 or f/2 it is just great for portraits and low light work. Not too sharp, but not soft either. Lots of "glow" in black and white. In good light I mostly shoot this lens at f/2 for depth of field reasons, but I really appreciate having an extra stop when I need it in low light.... which I frequently do.
By f/5.6 onwards it is a different lens - properly sharp and precise. I really value this for landscapes and detail shots. Because the character changes so much when stopping down, it's almost like having two lenses in one. I have never had a lens that changes it's character so much, and I find that I am considering this change of character for creative reasons just as much as depth of field. So it really is a lens that affects the way I visualise a scene. Hard to explain, and kind of weird for a "standard/boring" focal length, but it has wormed it's way into my brain for sure.
Criticisms....
1) It can flare spectacularly on occassion. I am talking about a full-on curved rainbow streaking across the bottom of images. I use a vented hood, and I only see this effect in very bright backlit scences, but it sometimes gives such a strange ambience to a scence that I just have to bin the shot or .
2) I wish it had a focussing tab ..... any ideas Brian???
3) No apperture stops, and they work in the wrong direction for my VF exposure meter. Not a deal-breaker, but something I would put right if I were designing a new one.
This is my first 50 sonnar, and I am pretty much in love with what it offers for such a small size. If I ever have the misfortune to do anything horrible to it, I would very seriously consider the ZM 50 sonnar because i love what the J3 has given me, but would like the above three drawbacks addressed. But unless I actually break the J3 I simply cannot justify the cost of a new ZM given my extreme satissfaction with the J3.
After my experience with the J3 I really do consider the 50mm sonnar design in general to be the perfect walk-around standard lens for me on a 35mm rangefinder.