The Phantom Blot.
Gaston, Ursula, and Cinderella’s stepmother.
the first two have terrific songs, too.
I’ll go with Shere Khan from The Jungle Book. He was voiced by George Sanders, and every word drips cunning and malice.
For Frozen, Prince Hans, for his excellent hard face-heel turn.
Well, a lot of my favorites have already been listed (Jafar, Ratigan, Ysma)… but… I can’t believe nobody has stood up for Captain Hook! Hans Conried in the role he was born to voice!
(I think Peter Pan was really sorta edgy for its day. Hook casually shooting one of his own men was not your typical kiddie fare.)
Hook was good, to be sure. But…he never really seemed all that threatening. He got played with the Tiger Lily in the rowboat affair, and he got just about the worst humiliation of any Disney villain. “I’m a codfish… Sob… I’m a codfish…” He just had too many handicaps (haw haw) and too few strengths.
I did like the scene where he tricked Tinkerbell into showing the location of the hideout, and, of course, sending up the bomb was a great move.
But at heart, the man was too much a coward.
Another vote for Maleficent. She’s got the complete villain package. Let’s look at the evidence:
Outfit - Black robes and horns
Familiar - a raven named Diablo
Motive - Didn’t get invited to the party
Action - Curses newborn baby to die
Bonus points
Alternate form -Black dragon
I thought Ursula was a great villain. Ambitious, she takes advantage of Triton’s weak link (Ariel) to try to overthrow him. Gives Ariel a faustian bargain that protects her legally from any intervention by Triton.
Triton himself came off as pretty incompetent. Dysfunctional relationship with his daughter, gets comprised by an old exiled adversary, sits out the final battle as a little weedcreature… Dude should have just let his daughter play with pipes and forks and make out with statues, went over and zapped that octopus lady before she got the law on her side 
Love Frollo–great villain, and I agree it’s because he’s understandable and believable. I can’t believe his whole story made it past the Disney board, but yeah, I adore “Hellfire.” One of my all-time favorite Disney songs.
My other favorite Disney animated villiain is Scar. “I’m surrounded by idiots!”