Chernabog; he's brutal.
(Same could be said for the Firebird in Fantasia 2000).
I'm just not a fan of Scar (anymore as much), though he puts on a good poker face. I actually do prefer his depiction in The Lion King live-action film.
I think Hades is less jokes and more personality than most villains. Doesn't have the issue of being upset over not being invited (a small issue), such as with Maleficent, which makes her appear more childish, imo. As ruthless as Maleficient is, it's the one thing (a party, and I'm not even sure if there's food being served) that ticks her off. I know Greek myths have Discord throwing an apple into a party to create chaos because she wasn't invited, but at least there was food and partying involved.
Cruella De Vil actually has a cool personality, but she becomes crazy over a simple thing (getting the Dalmatians) in the end and cries. A lot of these Disney villains need psychiatric help, imo.
And while I find Ursula, Mother Gothel, Jafar to be really good as villains, I can't say if they take the top bill for me.
I think the most rounded is probably Frollo in The Hunchback of Notre Dame; they explore a lot of different facets and seriously too; he's not a character joking around most of the time, unless it's circumstantial irony, such as when he's asking the guard to not shoot down his horse.