So tough between those choices.
I think both Lion King and Aladdin have excellent music across the whole films, with Aladdin my favourite of the two. Mulan is one of my favourite all time Disney films and the sound track has some of the best Disney songs, but overall isn't as good as Aladdin. The Jungle Book has some great songs, but are a little dated now I feel.
But I had to vote Frozen. I think it's taken Disney soundtracks to a completely new level.