Definitely the black OBS for looks...tough to tell mechanically b/c of high mileage...but if it were my choice, I would definitely get that black OBS. But really go over all of them with a fine tooth comb to see how well they have been maintained.
The NBS needs bigger tires/rims, it looks goofy with that lift and such small shoes. The Black OBS has a really nice stance with those rims/tires and the paint looks great.
But then again, I have a black OBS Tahoe so I may not be impartial!!