Pixar is probably the best animation studio working today, at least in my opinion. No one else really compares in terms of both overall quality and creativity. However, some of their films are much better than others, and a few of them just miss the mark entirely. Here's how I rank them, but what about you?
God Tier: WALL-E, Up, Inside Out, Coco
Absolute masterpieces of the medium that will be remembered for a long time to come. Beautiful animation, very emotionally touching content, deep and important themes.
Top Tier: Toy Story 1-3, Finding Nemo, Finding Dory
Great movies that should be seen by everyone. Very entertaining and emotionally moving, but generally lighter fare than God Tier.
Mid Tier: Incredibles 1-2, Ratatouille, Monsters University
Good, fun movies that are worth seeing for a diversion. Not particularly moving, but still artfully produced.
Low Tier: A Bug's Life, Monsters, Inc., Cars 1
Movies that are somewhat entertaining, but don't really go anywhere beyond that. Also, the first two are quite dated in terms of art and animation compared to Pixar's current standards, and it's noticeable.
Shit Tier: Cars 2-3, Brave, The Good Dinosaur
Pretty forgettable stuff. Either bore you or make you roll your eyes. Don't even show them to your kids.