I've pondered this question many times, having owned a silver chrome, black chrome, black paint, and grey finishes on my Leicas. I personally liked them all, but if I had to make a choice (a tough one), I liked the silver chrome the best, and the black paint the least. The black chrome is a close second favorite, though. It really depends on the day, though!
However, I personally just like the colder (more metallic?) feel of chrome on my fingers than the softer paint feel.
I use, though, they're the same to me. Whether I'm using a black chrome + black dot + black lens combo or a silver + red dot + silver, what really made me more "stealth" is how I acted rather than the camera I used. Smoother and "non-guilty" behavior did more for me than anythign else, and the more I shot on the streets, the better I got at this. (Although when I used an external viewfinder, I always seemed to attract more attention, stares, and questions). In all my years of shooting, though, I've never had any altercations on the street because of taking photos. Oddly, there was this one lady who insisted I delete the photo I allegedly took of her, when I really didn't (so I guess that doesn't count). Oh, for the record, I was using a Steel Grey M9 at the time, with a 15mm external viewfinder!