I think universally, it'd be hard to argue that there is a movie from Pixar that has as much to say as Wall-E. There is a long, long case study in that film. But even if you leave aside the climate politics, philosophies about how man deforms in the face of technology, the social retardation caused by devices and the inability to connect. All of which are backdrops to the essential story about Wall-E.
If you look at it at it's core, Wall-E has exceptionally little dialogue, and moves its plot along almost like a Silent film. There is a mastery of storytelling through animation, and the way the characters convey emotions through expressions and bleeps and bloops, takes Wall-E, thematically and dramatically to a whole other realm than the other films. That doesn't mean Wall-E is the "best". That is subjective. And just because the craftsmanship is beyond the other films, doesn't mean that you are only validated by embracing it.
But take a few steps back, and look, and really think about how many notes Wall-E connects on. It's awe inspiring. It's a film with so much to say.
I thought Inside Out was a good film, but it's scope is personal, narrow and more niche. They are to be applauded for tackling such a difficult subject matter. I cannot imagine many others getting a pitch through like that, saying they want to make a film that takes place inside a teenage girls brain. It sounds like the worst idea for a movie ever.
My personal favorite, the one that stuck a deep cord with me, was Ratatouille. I saw it with my class of kids I was teaching for (6-7 year olds, first graders) and many of them didn't particularly like it. I think it went over their head. They didn't really connect the jokes about the food, or understood what a food critique was, so I think they enjoyed it less. But for me, as an Adult I saw the personification of the judgmental of man, and how people with shitty lives act out their judgments on the internet. It being in a food context of the film is just the hat it wears. The concepts in the film are universal.
Posters on Gaming side of NeoGAF should be forced to watch that film again and again until they stop having meltdowns over silly video games.