I agree with the other members on this one. Looks great clean, but bad when it's not!
I owned a Jeep that was black and the very first time I washed it, I already started to see small swirl marks. I hated that about the black, the smirl marks. And you can't avoid them, they'll come no matter what you do.
Silver is probably your best colour for not seeing dirt and imperfections. Space grey is nice too.
It all depends on what you want. I'm sure with a new M3 in your hands you'll be happy either way.
