Grey seems more distinctive than the DSOTM, especially since virtually all other Speedmasters have black dials and bezels.
All-black watches seem a bit played out (just my opinion, much like my view of all black rims on a black car).
Grey looks more expensive than black--not that I'm into flashy watches, but an all black watch, given black watch ubiquity, sometimes looks a bit cheap. Not accusing the DSOTM of this, but I think there is a danger here. The Grey, on the other hand, looks classy to me.
Rarity of grey ceramic vs. black/charcoal ceramic. Most all other ceramic watches have been in black/charcoal.
I feel I'd have to dress way down to make the DSOTM work, whereas the grey seems more versatile.
The DSOTM seems too shiny for me, whereas the grey iteration is more of a matte look=much more under the radar.
Good luck with your decision.
Cheers,
John