I did a quick comparison between the Summilux 35 pre-asph and the Nokton 35/1,4 SC a while ago. If you go to our flickr site and tag "Voigtlander Nokton 35mm f1.4 SC" and "Leica Summilux 35mm f1.4". The two lenses are quite similar in character, both are sharp and medium contrast and compact. The Summilux is flare sensitive - later versions a bit less so than the earliest whilst the Nokton is very flare resistant ( it took me quite a while to even get it to show flare and that required that I took off the hood and shot almost straight into the sun). However, both are more flare resistant than the Asph S-lux.
There has been a discussion going on about the focus shift with the 35 Nokton. It seems that it has a shift at f2.8-f4.0. I have mainly shot it at f1.4 ( very sharp center) and at medium f-stops so I haven't found a major problem. All lenses have a focus shift somewhere in their range though - including the Summilux!
I would recommend the Nokton and depending on your film use I would go for the SC for bl/w and the MC for color, though both will do a good job with either filmstock. The Summilux 35 has become a "collectible" and the current prices in no way reflects on the optical quality! Some years ago they were $7-800 and a good deal (and no competition), today the Nokton at around $ 600 makes more sense and you are left with almost $1000 for film!
