Simply observe how a natural nest in a vertical cavity would develop, or not, as the case may be. Top down - always. The bees will always build from the roof and add comb for brooding at the bottom. They always store their honey directly above the brood nest. They would not start comb at the bottom and build upwards.
Look at Warre-type hive operation. Bees are left to build downwards with extra space added, under the brood nest, either all initially or as the hive fills with stores. Doesn't make a bit of difference when the space is added. Imagine a choice of them moving down into space or going back to some space, say a metre above the nest. No contest if the choice is there.
Now the beekeeper is wanting a product, often which is not in brooded frames, so the super space is always put in above the brood. Not quite the natural way to do it but closest to natural (await the TBH-only crews comments here!) is putting the new space nearest the bottom. It will have the advantage, on occasions, of getting the bees to draw the comb better because they are traversing the empty frames to complete the cappings above, so getting their scent all over it, so as to speak, rather than them ignoring space, right at the top, in favour of filling the broodbox as the main flow diminishes.
So, most comments in above posts are pertinent. In a large flow and only a couple supers it may not make much difference but if, say, there were 4 supers on, that 'new' space does not want to be at the top!
So fairly simple answer, when one thinks about the extremes (adjacent or a metre above the current brood).
Regards, RAB