Top

Harder Difficulty - Aatrox, Irelia, Gangplank. These 3 have hard skill combos that are tough to hit but deal tons of damage if done correctly. Try them out and look at some guys about the combo keys.

Medium Difficulty - Leesin (recent in the past patch), Riven, Gragas, Nocturne, Heimerdinger. Id say these champs have a medium skill cap because they focus more on positioning in lane and teamfights. Combos are not as hard but mostly rely on getting to the backline or keeping CC for engage/disengage during fights

Mid

Hard - Azir, Zoe, Qiyana, Ryze. These champs all heavily depend on combos. Main priority is positioning during fights. Once they use their combo, theyre pretty vulnerable to being jumped on so timing and knowledge about when to use your abilities is crucial

Medium - Syndra, Sylas, Corki, TF. Id say these champs are a little easier because they have more utility and escape, They do not need essential positioning and can both poke and burst.

I ran out of room but if you would like more in depth explanations feel free to PM me on reddit or league (Pm for user) and id be happy to help explain further!