I think it's funny this forum's obsession with the Chopin Etudes, but that's just me.
I still don't understand why everyone thinks that 25/6 is so hard.... But that's not really for me to judge. If your not used to thirds than I can see how that could be difficult....
And I really hate it when people say that the slower etudes are easy just because their..... slow. Some of the most complicated peices of piano repitore are slow. Each etude is just as demanding as the next in a different way. It's just however you were taught or whatever you've gotten used to.
The easiest for me was 10/9 "Opera". It's easier if you have big hands.
Hardest was probobly 10/1, Horowitz himself said that this one was the most difficult and 10/2 and 25/10 were immpossible. Then theres always 25/11 "Winter Wind" , the longest etude, which is the almost direct parallel to 10/12 "Revolutionary." Chopin thought that 10/3 "Triestesse" was the most beautiful melody he ever cultivated... I personally dissagree.
But still, the most difficult etude in technecal terms would definatly be 10/10. Sure, sure... it's never at the top of the list, but if you look close, this is the most difficult etude in whole op.10. Chopin tried to give this peice the widest range of "touch" that he possibly could in one peice, and to play it effectivly is even harder.
Then there are the slightly easier ones.
25/2 "Bees" isn't the easiest peice ever, but it most likely is the easiest in op.25. Then there's 25/8 "The Cello" a slower peice, but still difficult....
Gah, there are too many debates.
Anyways, my opinion:
Easiest(For me): 10/9
Hardest: 10/1