Obligatory plug of the Lyapunov Transcendental Etudes follows below.
These comments on the relative difficulties of 'Feux-follets' and 'Chasse-neige' could equally be applied to an argument about which of the Lyapunov Transcendental Etudes is most difficult - or, at least, which of the major key etudes is most difficult (No.2 in D-sharp minor, 'Ronde des fantomes', and No.4 in G-sharp minor, 'Terek', are strong candidates for the title of most difficult overall). No.9 in D major, 'Harpes eoliennes', features the same complex tremolos/runs as 'Chasse-neige', tremolos which interweave with the melody to create some very complicated textures. No.11 in G major, 'Ronde des sylphes', also features numerous awkward double note passages and requires feather light touch, as does 'Feux-follets'. So I suppose the more difficult of the two of those would be as much a subject of contention as the identity of the more difficult of the two Liszt Transcendental Etudes in which the tonic note is B-flat.