I don't really have a top five. I love them all.
But if I had to pick it would be this. (in no particular order)
The Land Before Time. Nuff said
The Land Before Time II. Mostly because Chompers in it.
The Land Before Time III. I have no idea why I like this one. I just...do.
The Land Before time X. Littlefoot meets his father and they have a flashback of his mother. It's cute.
The Land Before Time V. Chompers back!