I have played all three of them so if you have any specific questions, don't hesitate to send me a message In my opinion, the hardest is the last page of the third preludio. I have performed them several times and in this part you have to be very concentrated and relaxed at the same time, otherwise it's a real mess.I also agree with the other user - don't underestimate them. They're not very difficult as a whole, but they have many tricky parts.