Some of my impressions of the lenses you have mentioned:
A/Summicron Collapsibe: They are lower contrast than the later versions and they tend to suffer from scratched front elements. I never really got along with this lens(and I have had several of them).
B/Chrome Rigid Summicron: Classic look, well built and if you get one with clean glass, they are quite good. Depending on the vintage, the coating changed over the years and I find that the later (#2 000 000+) to be the best.
C/ Summicron 50 Dual Range: These are usually very good lenses, sharpness is up there with the latest 50/2's. It is the same formula as the "regular" rigid one, but they all came from the batches that were 51.9mm and I suspect that they were hand assembled and checked because of the inter lock for the close focus, The build quality is second to none!
D/ The later summicron's (post # 3 000 000) have upgraded coating, but lighter weight mounts. The aperture control ring in particular can crack as it is "poly carbonate" - i.e plastic. The "sep. hood" version has the advantage of having a focussing tab. Contrast tend to be higher than the previous versions but I have never seen any diffrence in resolution between version III and IV.
E/ The "collapsing" hood version (i.e the latest version) again is higher contrast and performance is very good (though the Zeiss Planar 50/2 is better!). I cant stand the hood on this lens as it never stays in place. It keeps collapsing and exposes the front element to stuff while in the bag! It also lacks a focusing tab.
F/ The Summitar 50/2. It is an old design and it does show in contrast and a certain "softness" to the image. This said, it is a nice lens and it has the least "fall off" of any of the 50's. Strong field curvature though and beware of sticking aperture blades and fungus. Flares quite easily too.
G/ Summarit 50/1.5: Soft wide open, an excellent portrait lens at f1.5-2 and quiet acceptable after that for general shooting. It does have low contrast and a bit "painterly" rendition in color (not unpleasant, just different). The hood is large and ungainly, but you really need it as it is prone to flare. It also has a strange filter thread so any non-UV filter (Red/Orange/Yellow etc) is difficult to find. The UV filter is not too rare. Very important on this lens is the condition of the front element and that it is "fungus" free.
Hope this helps with your choice. From a purely practical stand point, most, if not all of these lenses will do a credible job. My choice for a classic 50 Leica lens would be the Dual Range Summicron. It is heavy, but they are good. Try to find one with # over 2 000 000, as I have always found those the best. There was an improvement in the coating around that time. If you get the eyes with it, consider that a bonus, but it works fine without them, though with a 1m close focus, rather than a 0.7m of the later lenses.
