I think I've worked my way through 90% of the 35mm M lenses (except the lux asph), including the CV1.2, biogon, M-Hex, UC-Hex, 35 cron IV, 40 cron-C, 35 lux pre-asph. I've ended up with the 35 cron asph, but there's more to it than that.
2 lenses on my list would have been perfect for me but for one flaw. I believe the CV 35mm f/1.2 is the best 35 I've ever used (including a Canon 35L), but the size was too much for me on a rangefinder. The UC-Hex has my favourite signature and is stunning quality and build, but cannot focus down to 0.7m.
If I didn't take so many close photos with a 35mm lens, I would have stayed with the UC Hex forever. In the end, my cron asph "compromise" is doing me just fine, and I'm "done" with 35mm lenses.