Maleficent is my all time favourite Disney Villans...
Though I never classed her as evil, personally because I loved her character Lol. Though I can agree with her being the most sinister disney villan. She had an extreme sense of power about her and lacked the "goofyness" a majority of other disney villans had as well as possessing a deliciously, dark sense of humour.
Thing is, I had a problem when I was younger because I always sympathised with the villans. LoL To quote what the Kiddi Pickles said to her mother when Sleeping Beauty finished: "She wasn't evil. She was just upset because no-one invited her to the baby party".
Scar is also one of my favourites. Jeremy Irons had the perfect voice for that part.
He was cruel but possesses a brilliant, sarcastic charm about him. Jafar was close.
Shere Khan is in no way evil. Nasty, yes. Evil, no and certainly not menacing. I never really enjoyed the Jungle Book much either. It was an "ok" movie. Though I do love the Beatles as the Vultures and the songs are class.
Hades was just plain cool.
For me saying that Ratigan was "most" evil is just my personal opinion, I guessing because I'm going from the PoV of how that character made me feel about them. Despite the others being evil, I still liked them. Ratigan was the only Villan that made me feel angry and possess a true hatred for the character...There was nothing to like about Ratigan at all. He wasn't funny, he certainly wasn't nice, everything he did was evil for evils sake or to get back at Basil and his voice (provided, of course, by the great Vincent Price.) attempting to be suave but just shouts "EVIL GENIUS SLIMEBALL"!
Lady Tremaine comes in very, very close second, there was nothing to like about that woman either, i think what was worse was the fact she always reminded me of someone I knew.
Ursula will be my 3rd choice, I always hated that octopus witch.
Bambi and the Lion King, though they had their sad moments they weren't the saddest. The Fox and the Hound was the only Disney film ever to make me cry....only ever watched it once LOL can't even remember the story.