Most of us probably voted for whichever one we own!
I'll go for the collapsible because (a) it's the only one to work on an M and an LTM and (b) it has an old-world charm that the later ones don't. The collapsibility, incidentally, doesn't make it *that* much smaller; it's a lot bigger than a Summar of the same maximum aperture, and positively huge compared to an Elmar f/3.5.
I also like the muted contrast of the older Leitz lenses - they are pin-sharp (even that Summar) but you don't lose the shadow detail as easily.