I did a partial, quick comparison, out of curiosity, and can say that, for the most part, I would prefer the Brandus/Billaudot for clarity (although their 32nd note beams are too thick and tend to merge, in prelude no. 24). There are several places where material that is on one page in the Schlesinger is spread over two in the Billaudot, which helps readability. There's a clear key sequence in the Billaudot (pairs of preludes ascending in chromatic half-steps), and for some reason, the Schlsinger is in a different order. In "Un petit rien", Billaudot has both turns and mordants as ornaments, Schlesinger has only mordants and no turns. Since Billaudot made the distinction, it seems to me that it is probably correct (but that's just an assumption, of course) .
And finally, there is one discrepancy I noticed that's amusing. In "Rêve d'amour", at a spot around halfway through the piece, the Brandus/Billaudot edition has a marking of "avec volupté". The Schlesinger has no expressive marking at that point at all. Was the idea of voluptuousness in a dream of love just a bit too racy for them to handle?