people's favorites tend to be 1 and/or 3. 2 was criticized as too complex, narratively, and was also the only one where they travel into the future (1985 -> 2015), which makes the context incorporate more elements of speculative fiction like social critique, suburban decay, poverty, and inequality.
it portrayed a future America that was, if looking beyond the technology and spectacle, actually pretty bleak. the dream home/neighborhood of their younger days had become dangerous with violent crime and overpoliced, bosses were cruel and exercised total control over workers. cultural production had ceased (legitimately an ad for "Jaws 19"), and wealthy bullies seemed to still plague public spaces.
i was a sci fi kid so i was fascinated by the dip into the future and the alternative timeline plot points, but everybody else in my family said it "sucked" and much preferred the more palatable wild west movie as well as the original, which could have nostalgia for america's past but ultimately brought us back to a better present and the impression that everything is always getting better.
looking back now, Back to the Future 2 was grimly prescient about the social reality of america.