Still a bunch I haven't seen so will obvs just rank what I have:
1. UP (Classic simple story and great characters/animation)
2. Toy Story Trilogy (as above)
3. Inside Out (love the concept and the wacky and colourful animation; brilliant acting as well)
4. Wall-E (love the concept and animation of this one)
5. Brave (not a classic story-wise but I love the characters and over-all style; plus it gets bonus points for representing Scotland)
6. The Good Dinosaur (again, not a classic, but the contrast in it's beautifully rendered realistic backgrounds with stylised characters does enough for me. Plus it's a lovely simple story)
7. Cars (nearly missed this one. A bit gimmicky if you're not a car buff, but I loved the story of this one. The second film was a let down in my opinion)
A Bug's Life
Animation wise these are great (although if you look at A Bug's Life now it looks really rigid compared to the latest offerings since it was made many years ago), and I can see why they're popular/classics but personally I just either wasn't into the stories or characters enough.
Hmmm... can't say I can't put together a comprehensive list as I feel I've grown out of many pixar films and haven't seen a bunch of the newer ones, I don't know many people so no one gets me to watch them
I will say though bug's life was one of my faves growing up and toy story 3 still sticks in my mind for that incinerator scene, the writers must have some people break up with them so they put something out into the world they knew was going to hurt.
For some reason, the internet wants me to watch the start of UP