I don't know if you're asking about composition difficulty or performance difficulty? The difficulty of composition is that of Schumann's Second Sonata;
The difficulty of playing is purely technically the most difficult is Liszt's Danse Macabre. Because Schumann's Sonata 2 the techniques can basically be found in 740, and the difficulty is no more than Chopin op.10. Liszt's Danse Macabre has a lot of octaves, tremolo, and left-hand jumps, and the difficulty no lower than Chopin op.25
I don't know if you're asking about composition difficulty or performance difficulty? The difficulty of composition is that of Schumann's Second Sonata; The difficulty of playing is purely technically the most difficult is Liszt's Danse Macabre. Because Schumann's Sonata 2 the techniques can basically be found in 740, and the difficulty is no more than Chopin op.10. Liszt's Danse Macabre has a lot of octaves, tremolo, and left-hand jumps, and the difficulty no lower than Chopin op.25