Summicron - Great great performer for it's price. Smallest of the lot, if you don't need speed the this is your glass of choice.
Summilux - Best lens that leica made at this focal length, been with me 5 years and I haven't owned anything else in ages as I can't afford it.
Summicron APO - used it at the M Monochrome launch, and despite it's long backstory - it was very sharp, wide open but probably not worth the extremely high premium IMHO ($10000 and above) and also, claimed to be the most perfect lens ever made by the staff.
Noctilux - I am a film user primarily, and due to my shooting style I rarely ever do shoot wide open, mostly at f/5.6 - 8 at pre set focusing for ease of shooting. With my camera, I also cannot make use of the len's speed due to slow top shutter speed of 1/1000. If you own an M9/M240, go for it as it's an insane lens. Rendering is beautiful, but softness is expected. Not a bokeh fan, but its really very nice and creamy. If you use film, it's probably not so smart a choice as you don't wanna risk your images being OOF because it is quite tricky to get your focus, it's really really shallow wide open. Size wise it's huge, heavy. Not an everyday lens if you ask me, the chance of it being stolen/damaged just makes me quiver.
My two cents worth!