That's a tough choice. While I love the 75 Lux, I've seen some stunning photos from the Cron -- super sharp in focus with beautiful bokeh. One advantage of the Lux is you can change the character of the photo quite a bit by changing aperture -- from soft and dreamy wide open to progressively sharper stopped down. The Cron seems to be more consistent across the range of apertures.I'm in the process of changing my lens kit and am considering the 75 Lux or Cron. I will mostly use this focal length shooting inside at a couple of our local clubs that provide music entertainment.
I sure hope I'm never forced to pick on. Of my current crop I have no idea which I would pick. Probably the 50 Summicron, but the 35 Summarit might get the nod. I'd pick one of my Sonnars, but don't know that I'd want to trust something that old as an "only" lens.That's a lovely lens. If I were forced to pick just one, I think that'd be it.