With the exception of the Cars trilogy, there aren't any Pixar films I actively dislike. For everything else, it's just a matter of degrees. Some of them are exceptionally brilliant... others are just really good animated features. Here's my ranking from favorite to not-so-favorite...

1. Monsters Inc. In my mind, there's no more perfect Pixar film than this. Compelling story. Loads of humor. Amazing characters (including Sully, my favorite). Everything I love about Pixar in one movie.
2. The Incredibles The best Fantastic 4 film yet made. And, until Marvel Studios hit the scene four years later, one of the best super-hero films ever made. The architectural style of this film is over-the-top beautiful.
3. The Incredibles 2 More of the same. Which would usually be a bad thing... but they pushed it into another level of brilliance.
4. Toy Story 2 I was mortified when I heard there was a sequel happening to Toy Story because I was convinced most sequels were crap. Boy did I get proved wrong. A brilliant follow-up that actually improved on the first one.
5. Up Pixar has a way of putting a lot of heart into their projects. This is probably the film that tugged on the most heartstrings for me. And, as if that wasn't enough, they went and put Dug in there too.
6. Toy Story The film that started it all, and Pixar completely knocked it out of the park.
7. Toy Story 3 A lot of people put this at the top of their list. It's easy to see why, but it felt a little emotionally manipulative and deliberate to me. Still an amazing film.
8. Finding Nemo What I love about this film is how beautifully the story all came together. Sure it looked good. Sure the plot was clever. But it flowed so naturally from scene to scene... from moment to moment... from start to finish.
9. Coco One of the most beautiful movies ever made. If the story wasn't so overtly manipulative, I probably would have ranked it higher.
10. Wall-E I think my expectations were too high here. It was a wonderful film, but I had a tougher time buying into the story than I probably should have given that it was about robots. I can say that it had the best end-credits of a Pixar film.
11. Monsters University A terrific flick, but it seemed like a missed opportunity to go back in time for a prequel. Nobody could come up with a sequel idea worth working on? Even so, Sully remains my favorite Pixar character by a wide margin.
12. Brave A movie that's insanely gorgeous to look at, but kinda fell apart for me story-wise. Merida seems short-changed, which is a shame, because you can tell they were trying to push the idea of "Disney Princess" into a better direction.
13. Finding Dory I'm not entirely convinced this was a sequel worth telling. But, then again, it was still a really good movie.
14. Inside Out This is consistently one of the best-rated Pixar films... and I get that. It's a beautiful, heartfelt story, but it also has a level of detachment to it that made it tough for me to buy into.
15. Ratatouille Cute characters that are beautifully rendered. But the human characters, particularly the lead, dragged everything down for me.
16. A Bug's Life It would be easy to say that this movie hasn't held up well, which is why it's so low on my list. That's not entirely true. I think it's just as visually stunning as it ever was. The voice acting and story are entertaining. It's pretty fantastic so far as cartoon movies go. But when compared to all the other Pixar films? It's a weak link for me. Didn't dislike it, just didn't care for it as much as others.
17. Cars I couldn't get into the world they were building here. Anamorphic cars just did not work for me (surprising given my love of the Chevron cars), and I didn't care for the story much to boot.
18. The Good Dinosaur It's not that I hated the film... it certainly looked pretty... and it's way above other cartoon crap... it's just that it lacked the multi-level appeal that allows adults to find fun in a juvenile film.
19. Cars 3 So bad. I was bored, bored, bored. Repetitive and dull from start to finish. Can't believe this got a theatrical release.
20. Cars 2 So very bad. This was the movie that convinced me that Pixar's magic was in serious decline. The reason I place it dead-last is because of the stupid-as-shit "spy" plot-line. Fortunately, Pixar regrouped and got their crap together. But that didn't stop them from releasing Cars 3.

Next up is Toy Story 4. Not exactly sure that was a smart move given how nicely things got wrapped up in the last one, but I'm trying to keep an open mind.