Recently watched all the Pixar movies, this is my ranking, Ratatouille being my favorite.

S: Ratatouille, Toy Story, Coco, Toy Story 3, Inside Out, Soul

A: The Incredibles, Cars, Up, Toy Story 2, Luca, Monsters, Inc.

B: Finding Dory, A Bug's Life, Finding Nemo, Brave,  Incredibles 2, Toy Story 4, Onward, Turning Red, Inside Out 2

C: WALL-E, Cars 3,  Monsters University, Lightyear, The Good Dinosaur,  Elemental

Cars 2-tier: Cars 2

5. Toy Story 3
4. Monsters Inc
3. Toy Story
2. Toy Story 2
1. A Bug's Life

5. Monsters Inc
4. Toy Story 3
3. Soul
2. WallE
1. UP

Honorary Mentions: Toy Story 1/Finding Nemo

With 1 being the very best and 5 being the 5th best. Tho to be honest the first 3 could switch places between themselves, all 3 are goated for me for diferent reasons, its really hard to place one of them above the other. 

Wall-E

This movie is on a level of its own. To me it shows what happens and what gets destroyed in unchecked free capitalism. (Our environment, our resources, our planet, our sense of wants and needs,...)

And how that leads to communism. And it shows what happens and what gets destroyed in communism. (Our society, our inter-personel relations (the only relation we need is to the government), our knowledge of the world and the things in it,...)

And it is even hopefull enough to hint at a way out of that sorry state.

That is not even mentioning the designs, the show don't tell approach, the AI aspects, the meditation on lonelyness, the trope reversials not feeling forced and just there to subvert expectations, ...

Truly a masterpiece and a movie way bolder than anything getting produced these days.

Cars. I love the original and rewatch every year on March 20 for some reason.

Monster Inc, took three different dates to it in the span of a few weeks.

Wall.E

I generally don't like Pixar films.
That said, Coco is the best by far, followed by Inside Out.

Inside Out and/or Wall-E.