User blog comment:BerryBandit/Mechanically demanding champions/Quick decision champions/@comment-6927690-20130628163827

For an ADR, well, it depends. If you see the way Doublelift plays his Caitlyn, or his Vayne, you'd notice that the thing that separates good ADRs from the great ADRs are moving in between auto attacks.

For Mages, I'd say Zilean for the reaction time(of the R, unless you know, you're lazy and prime your R on the onset) and his burst / chain debuffs (E-Q-W-Q-E), Kayle for the prediction and judgment calls (of the R again). Zed to an extent (W-W-R-Botrk-E-Q / R to chase).

For supports, hardest would be Janna (make or break ult, clutch Q to interrupt dives, clutch shields). Thresh (if you want to pull off perfect coordination with Q and W).

If you're looking at mechanically demanding, try Syndra in an extended clash. Leblanc to an extent due to her combo-ish nature. I wouldn't say Elise, because she's what I'd call a "piano champ" (human E as an opening, when it connects, mechanically Q-W-R-Q-W)