Thanks for your replies. I read some (let's say "a lot" about the different lenses, and I'll be going for a Summicron as my first lens.
My intent is mainly street photography, to supplement my 'flex, and the wide aperture and better ergonomics seem important to me.
The one I'm lusting after is from 1990, so I guess I won't be disappointed by performances.
I'd like to put in my vote for the version 4 summicron; the same optically as the current non-APO summicron, and it uses/needs a clip-on shade. I think those provide better impact protection than a pull-out shade.
I photograph things to see what things look like photographed.
- Garry Winogrand