I believe they can coexist in one's collection.

If I could only choose one, it will probably be the black Black Bay (they finally matches the name with its colour,

)
The Black Bay is more versatile, all rounder watch - auto winding, sapphire crystal, and higher water resistance.
I would buy the new Black Bay in a heartbeat if it was a little thinner and a little cheaper.
A pre-owned moonwatch is easily the best value buy out there.