See previous discussion on how to choose a 50mm Leica M lens.
The three Leica “bad boys”, all with different personalities.
A enjoyably large version of this image and others is found in Guide to Leica on the 50mm Lenses page.
Leica 50mm f/2 APO-Summicron-M ASPH
Leica 50mm f/1.4 Summilux-M ASPH
Leica 50mm f/0.95 Noctilux-M ASPH