I picked Lion King because that soundtrack is full of pure classics: Circle of Life, Hakuna Matata, Can You Feel The Love Tonight etc.
Aladdin, Jungle Book and Frozen have pretty good songs too after saying that. I know Frozen's 'overrated', but you have to admit, it's the first Disney film to have some really iconic music since the new millennium.
Never seen Mulan so I don't know any songs from that film!
Then again, lots of Disney films have such good songs..