I love this topic! I don't have a 'favorite' anything, but off the top of my head, I'll say
Yellow Submarine (great music, great message, total acid trip of a film)
Watership Down (and ONLY the 1978 version), "Oh, here's a fun, animated film my kid will like! Let me turn on the tv and they'll love it!" - traumatized a generation. But what a heroic story! What a tear-jerker! And now, I watch it in tribute to Jon.
Not to mention I was raised up on an endless string of Rankin and Bass TV specials. Clunky, sappy, and we LOVED THEM!
Amongst the long amount of holiday specials, they also did "The Hobbit" and later on, "Return lf the King" who knew orcs could sing with such a fine baritone? 😆