Mineral Grey. Don't be stupid.
I just came off an E90 in Space Grey, and I too was concerned that the colors may look too similar and that I'd be bored. Mineral Grey is much, much deeper really reflects light beautifully, looks black at night, is really one of the best grey's BMW was ever made.
White F30's don't look as nice, all the beautiful curves in the sheet-metal creates no shadows, it all gets absorbed in a big sea of nothingness. Mineral Grey really reflects the light, see photo above, you have to see it in person understand.
Here's the official F30 Post color threads, have at it.