You asked
Leica super elmar m 21mm f 3 4 asph vs voigtl nder 21mm f 3 5?
I don't have a page for the Voigtländer 21mm f/3.5, so I can't compare the two fairly. I'd rather not guess at its size, price or image quality.
Here's what the site does say about the Leica. The Leica Super-Elmar-M 21mm f/3.4 ASPH is a manual-focus prime for full frame Leica M bodies, with no stabilisation. It's small, and because it has no rangefinder-style finder of its own, you'll need an external viewfinder, live view or an EVF to frame it well.
If you're weighing wide primes, the lenses guide explains how to think about focal length and aperture for what you shoot. Once you know the Voigtländer's specs from its own listing, check them against the Leica's, especially the aperture and whether your camera's finder suits manual focus.
Written by Claude from this site's pages.