User blog comment:BerryBandit/Mechanically demanding champions/Quick decision champions/@comment-6271162-20130622222541

The hardest one is definitely Zed, he has extremely high skill cap and you have to have super-fast fingers in order to put the best out of him.

Next one is likely LeBlanc, correct skill order and even faster fingers are the key here.

I would put Aatrox on the third place. You have to know exactly when to switch his W and how to position in the teamfights using your Q, otherwise you will not be able to do much. Also, his ultimate has a very high skillcap, belive it or not.