While the black paint version is certainly a beautiful finish when the camera is new, I just don't understand the allure of having a camera body that brasses at a somewhat accellerated rate. Does a worn black body imply that the photographer is more professional because it shows signs of heavy use? I find it amusing that Leica offers a finish that can make the camera appear more well used than it actually is. For what reason? Unless you truly like the look of a well-worn camera, the remaining reason appears to be that some are more concerned with the outward appearance of the camera and what kind of "photographer image" that they project toward others. Poseur jewelry, IMO.
I use my cameras every day, and while I don't baby my equipment, I don't beat the crap out of it either. My cameras are the tools of the trade and I take care of that investment. If I show up at a job with a bunch of worn out looking equipment, that appearance doesn't neccessarily instill confidence in my clients. I some circumstances, it could be taken in a negative manner, (i.e. "That photographer must not be very sucessfull -- poor sap can't even buy a decent camera.") If I'm shooting a wedding, I wouldn't show up with a dirty vehicle. Likewise, I don't think that worn looking equipment tells others that we are more professional. You don't always know how you are perceived by others.
O.K., so what it boils down to is this -- what personally looks good to you? If you truly like the look of a brassed body, go for the black paint. If you want something that will look good with prolonged use, you can't go wrong with the chrome version. If you want black and durable, the ala carte choice is your only option. Too bad Leica doesn't provide a finish like the black paint with the durability of a plated finish. In my book, that would be perfect, but of course, everything is a trade-off.
Whatever you choose, enjoy your camera -- the MP is one heckuva nice piece of equipment!