For Disney I always liked that rough and shitty era in like the 70's-80's, pre-Eisner. I like the scrappy-ness of those films! Shoutout to Robin Hood, The Rescuers, Great Mouse Detective in particular. I'm much more interested in non-Disney work though. Here's some picks I love, I'm gonna include anime films too because i dont give a shit:
The Tale of the Fox (1937)
Fritz the Cat (1972)
Fantastic Planet (1973)
Son of the White Mare (1981)
The Secret of NIMH (1982)
The Last Unicorn (1982)
Night on the Galactic Railroad (1985)
Felidae (1994)
Catnapped! (1995)
Malice@Doll (2001)
Waking Life (2001)
A Scanner Darkly (2006)
Legend of the Guardians: The Owls of Gahoole (2010)
Rango (2011)
It's Such a Beautiful Day (2012)
When Black Birds Fly (2016)
My Entire High School Sinking Into the Sea (2016)
Loving Vincent (2017)
The Wolf House (2018)
Also for more avant-garde shorts you gotta check out the work of Stan Brakhage, Takashi Ito, and the Brothers Quay. Mindblowing and classic stuff