Hard to say.
IMO the 35 Summilux has a very nice drawing and Bokeh from what I saw in images posted in the net.
The 35lux-asph is quit sharp and has a nice contrast without being clinical, and also a nice bokeh. Many samples seem to have focus shift which makes it hard to control them.
The full frame sensor means even shallower DOF wide open so I am not sure if one can really take advantage of this lens (because its just to hard to predict where to focus at which f-stop)
Thats why I havent used mine much.
Then there are (older ) 35crons - very small size, good image quality, wide open maybe not as sharp and contrasty as asph lenses. Some can not be coded-but with the M9 thats less of a problem since you can set it manually (you should not forget it though)
I will experiment with my 35cron on the M9-I really like the small size and f2.0 might be fast enough for me.
And then the 35cron asph. Probably the safest way to go - good compromise regarding size, price, drawing, and as far as I know no focus shift problems.
If I had to buy a new lens today I would first check how the 35 Summarit performs on full frame, and if 2.5 was fast enough for me. If yes I would go Summarit, otherwise I would go for a 35cron.
IF (and thats the big question for me) one can master the 35lux_asph (or if there are samples without focus shift) than it would be a great lens, but IMO with the FF-sensor f2.0 or ven f2.5 should be fine as well.