I have SSII, so I can give you my honest opinion... and you can believe it
. I was expecting a silver color, so I was a bit disappointed when I saw the car. Color looks great, although a bit feminine IMO. But after a testosterone injection in the form of black OEM 19s, black OEM grilles, black muffler (but chrome tips), tinted windows, reflectors shaved, and body-colored gills, I'm quite happy with it now. And I'm glad I bought it, because if I had seen it before buying, I'd have searched for AW instead, and there're TONS of those around, and in every model BMW makes.
The other thing you need to consider is SSII is the cleanest color in the M3 pallete, while SG is going to show dirt a lot. Not a huge deal, but another factor to consider. Good luck.