In terms of "difficulty" in ascending order, I find Chopin etudes far more tricky than etudes by Rachmaninoff and Liszt. Maybe not to sightread, of course, but to get the ultimate artistic result.
Come now. Here in my conservatory I know a lot of people who are taking up Chopin etudes, but only the best of us could do the Wilde Jagd, and even that performance was not that clean.
And everyone says Feux Follets, Chassie-Neige, or Mazeppa, are some of the hardest works ever.

I was in the music shop near the China Conservatory of Music (or was it the Central?) in Beijing a couple of years back, and bought a CD of the Transcendental Etudes recorded by some 14 year-old Chinese kid. The CD booklet-thingy said that he learnt and memorised all 12 in 2 months, and had already recorded the Chopin etudes (if I remember correctly)...fuarq.
There are so many of these Chinese prodigies that I have to remember that it's actually futile to be measuring
myself with the world.
And always, my reaction would be: "Well then, with talent like this, we hope he bests Arrau or Horowitz in the long run."
