Another vote for the black Canon 135 f/3.5. It is compact, light, and very nice sharp pictures, with excellent blur. I own the Steinhel f/4.5 in LTM, the Contax RF CZJ 135 f/4, and the Canon 135 f/3.5 in LTM; I've handled the Leica 135 f/2.8 Elmarit, the Nikon 135 f/3.5 in Nikon RF mount, the Leica 135 Elmar f/4...
If Contax had made the 135 f/4 Sonnar in LTM, I'd choose it over Canon's, for it is slightly more compact, and of course, takes beautiful Sonnar shots.
For Leica, all things considered, no doubt about it, I say get the black Canon 135 f/3.5.