Possibly a controversial opinion, but I don’t think Pixar has made a film that was more elegant and complete than Toy Story. They’ve addressed bigger ideas, in more ambitious settings; but Toy Story is the building blocks of many of their other stories without any fat.
If you haven’t seen Toy Story, I’m at your door with the DVD* right now. So let’s not bother with recapping the storyline. The film is obviously built around the conflict between Woody and Buzz. Woody is a catastrophist with low self-esteem, and Buzz is the polar opposite: an egotist who is so wrapped up in his own world that he’s basically the only toy who DOESN’T know he’s a toy. Naturally, all the circumstances aside, characters who are opposites tend to clash.