Each one has specific reasons but they are all good, but I have to say Peter Pan has the slight leading edge. Great adventure story about something that effects us all: growing up. I think the next one in line has to be Alice in Wonderland. I always enjoyed this one because of its bizarreness and never found it dull or boring.
I really chose Lady and the Tramp because it defines a different look at film. Life from the point of view of pets.... and these pets are the ultimate Disney animal characters where the animals act like animals. It really is a great script.