I was going through this choice, too. The car-builder on the website makes the grey look a lot darker than it really is. I thought it was a dark grey/pewter sort of color, which would have been a nice, but not too big, change of pace from my last two black cars. But then I saw in-the-wild photos and drove one on a test drive and was surprised how light it was. One both me and my girlfriend thought was light blue (until I remembered that wasn't an available color).
Then again, I've always been a "but the layer of dirt will protect the clear coat" kind of guy so keeping it perpetually waxed has never been a concern of mine. (I didn't even know swirl marks were a thing until reading this forum!
) Plus, here in Lubbock even the best wax job is covered in dust within 10 minutes.
I'm doing research on waterless car washes, though. Would a good wax coat, clay bar, or whatever make it easier to do something like "dust" the lighter stuff off the car, making it easier to go a while between actual washes?
Back on topic, I agree with texex91, gotta go black. Even a little dirty, I imagine black would still look good. Seems like grey would just look "meh" unless it's car show polished.