I guess it depends if people call those "Disney Renaissance" movies classics, from the late 80's - early 90's. Those were ALL great - Little Mermaid, BatB, Aladdin, Lion King.
Taking those out, I'd have to go with Toy Story and Ratatouille. I think Ratatouille is one of the most underrated Disney movies even though it gets 4 stars from a lot of sources - it still doesn't get much attention. And I'm someone that prefers 2D animation and the older Disney stuff. I think there's a lot of wisdom in that film too, which a lot of movies seem to lack lately.