That might depend strongly on the filling-in details and on how the choice is framed. I can't visualize all the options and compare them together, so I always end up comparing the nearby cases and then running through the loop. I suspect that forced to make the choice I would say An (the dust specks) but more because of it being a Schelling point than any substantial, defensible reason. And I would say it while still endorsing A(n-1) to be better than An.