The ones the Disney brothers and the Nine Old Men worked on (Snow White, Pinocchio, Fantasia, etc.) and man, the animation is fiendishly smooth. It holds up better than most stuff that's been animated between now and then despite being so much older. I can scarcely believe human hands animated these movies. The insane amount of work and polish that went even into the first one, Snow White, is insane. The complexity of the facial expressions alone is a technical marvel.