I "chose" Mineral Grey for the same reasons mentioned above. Metallic paint is (hopefully) more scratch resistant and I just like that metallic look of it. Also, MG is very very nice color to my eye
I don't really like white cars, it's a bit like my wife says: they all look like taxis :P And also, they're soooo popular now at least here in Italy, so it would totally not stand out at all.
Non-metallic black in turn is difficult to maintain well (getting into detailing here.. already feel sorry for my wallet). Also, IMHO, the 1er looks even smaller in black, and the 5 door version does not have enough chrome trims or other details to contrast the black.
Anyway, MG was my number one choice for color right from the start, and then it just so happened that I found a good offer for car and it just so happened to be MG
Luckily it's not too common a color around here.