Choosing is personal thing depend on what one's need in "lens rendering".
Comparing Leica lenses from different versions is something very hard and loss effort anyway.
In the past, I had no choice of 35mm Summicron for M.
My first was the version IV in '80's.
Over time, I have/had other versions of 35 Cron.
A phrase to differenciate them from my own experience over time:
Version I (dixit 8 elements) soft with little contrast at f/2 and much better contrast from f/2.8 and very good after that
Version II and III same optical 6 elements more contrast at full open and almost equal from f/2.8 better "flat field" but less "romantic than 8 element"
IV (7 elements) is another step (not much) in contrast full open,
Asph. version is the best contrast rendering at f/2 and keeping that closed down
each version is different and as good from about f/4 or f/5.6 on 3 dimensions subjects.