I was under the impression that it was the hardest.
Oh no way. The fourth is a good bit more difficult.
I agree that the 4th is more difficult; my only problem with the 4th, however, is the 2nd movement ........ it strikes me that the 2nd mvt is a mere intermezzo movement, a mere transitional movement from the magnificent 1st movement to the sublime finale ........(am I missing something?)