League of Legends (LoL) Question: On which champs/cases is athene's better than morellonomicon

Basically, Morellonomicon is for a full, mana-sustained APC, i/e someone either without much in the way of mana issues, someone you don't mind managing your mana with, or someone you've already build a tear of the goddess on and need solid AP/CDR. Athene's is more in the way of a defensive/utility item due to the MR you get, and both the mana regen stat boost and the mana font passive. Unless you are playing a champ with serious mana issues, or youd just like to spam abilities with some more survivability, go Morellonomicon. If you're playing a seriously mana hungry champ and don't want to build TOTG, go Athene's as a second item. Or if you're galio.

The answers given so far are pretty good, but never did answer the champ part of the question.

Hands down, Galio benefits off of Athenes more then anyone, because of his passive. There are some supports that may benefit more off of it then Morello.

Usually Athenes is better when facing another AP midlaner or if your champion has SERIOUS mana issues, but if you want to play more aggresive or you are against an AD assasin per say, you will likely want to get Morrelonomicon instead for the extra AP and more cost efficiency. This can vary from champion to champion, some champions like Galio get a much larger benefit from Athenes then Morrelonomicon overall but this isn't always the case.

Actually, Morellonomicon is a solid choice if you are winning the lane because it gives you more AP and it's cheaper than Athene's Unholy Grail.
Usually,if you are winning the lane and doesn't need the mana regen,you buy Morellonomicon
But,if you are losing or you just need some MR against LeBlanc and other AP Assassins,you buy Athene's Unholy Grail
Also,you can buy Athene's Unholy Grail if you are Galio.

TL;DR: Morellonomicon if you are playing offensively, Athene's Unholy Grail if you are playing defensively

Excuse my english,it's not my native language :c

Well morello just got nerfed, i guess morello is usually better because more cost efficient but athenes can be good vs an AP midlaner and for a player who doesn't want to have to manage his mana