I used to be of the black on black school of thought, but now I'm not so sure. My M-P 240 Safari set is chrome on olive green and I really like the look. My M4-P is black chrome, which I also like.
Sooner or later, I will acquire a Monochrom typ 246 which just became available in the la carte (bespoke) program. I may opt for either gray leather on chrome or the traditional black leather on chrome. A little variety is a good thing, even though the traditional blackout treatment on an M camera may be more tactical for street photography.
In terms of durability, I have read that Leica's chrome plated finish (not the silver paint) is the most durable of all finishes that are normally available (titanium is only offered on select limited edition cameras as I understand it).