I'm going to re-watch AHX again before I vote (or post about it), but I can at least talk about Toy Story 3 with some level of knowledge. I get that a lot of people like the first one more - some even like the second more - but for where I was in life when TS3 first came out, I thought it was a masterpiece.
1.) It showed the growth of Pixar from its very first feature film, to where they were 15 years later. A lot happened in 15 years, both from an animation standpoint, and in the depth of their writing and direction. So much happened between Toy Story and the release of Toy Story 3; we're talking Finding Nemo, the Incredibles, Wall-E, Up, etc. Some of the greatest, most well-done animated films of all time. And then Toy Story 3 comes out as this sort of...cornerstone on the last 15 years of brilliance.
2.) It showed the growth of the Pixar viewers throughout the years. I was 5 when Toy Story came out. It was one of the first movies I saw in theaters (since then I've seen all of Pixar's films in theaters). I was at the age where I played with toys all the time; I may have even had Woody and Buzz action figures, I don't remember. By the time 3 came out I was gone off to college (I actually saw it on the lawn with a few hundred other people). The movie was about more than toys, it was about growing up and moving into a new stage of life. And that the things we leave behind will fall into place, embracing a new generation right behind us.
I'm fully willing to admit that the timing of TS3 lining up with my own personal experience is why I love the film so much. But I can't really remove myself from that. Even so, it's a phenomenal film with a stellar cast, and went in an emotional place that is rarely traveled by animation.