I have a 35/2.4 summarit and the CV 35/1.7 ultron
I only shoot digital these days though
Of the two I use the Ultron more.
The CV vignettes more and the summarit has more visible distortion
The summarit is a nicer shape, is a lot smaller (it’s tiny without the hood)
The CV is bigger, has frankly a very strange shape, with a weird shaped focus ring
The colour signature of each is pretty similar
I feel the Voigtlander is sharper, the extra stop it has over the Leica is very welcome
Neither lens is particularly prone to flare
My CV cost new ex-display about half that of my summarit as a dealer bought secondhand item
If I could keep only one it would probably be the Voigtlander
Final opinion..
If (IF) you can live with the size and strange shape of the CV 35/1.7 it offers you a little more performance than the summarit at a lot less coin
The Leica lens is coded for Leica digital (and the LR lens profile corrects the distortion, but the C1 one doesn’t) but that’s pretty irrelevant for film shooters I guess…
The biggest performance difference I see between them is wide open/close to wide open (the CV is basically a stop faster), so if you’re an F8 and be there kinda shooter, then don’t put too much stock into this