Prisoner of Askaban is my absolute favorite.
Harry Potter
Prisoner of Azkaban was a more chill book. Without the impending threat of Voldemort, it explored the more fun side of Hogwarts. Sirius Black's plotline was one of the best parts of it.
I agree totally, it just seemed more magical.
Its a close one between 4, 5 and 6, but I think Order of the Phoenix takes it. There's a lot going on that year with the DA, Cho and the ill fated trip to the Ministry.
Prisoner of Azkaban was my favorite for that one shining moment of hope for Harry, that he could live with someone who knew his parents, loved them, and loves him. The hope was dashed too quickly though, I cried harder when Sirius died (in order of the Phoenix) than I did when Dumbledore died.
Half Blood Prince.
After the sheer drudge and endless torment of Phoenix, the comedy fun and frolics of "Prince" was just a welcome relief.
Closely followed by Goblet of Fire and Chamber of Secrets.
OOTP and Azkaban are way down the bottom of the list, simply because they are too damn long. (The end of Azkaban seems to be longer than ALL the other books combined, which I realise should be impossible but trust me -- it is).
Harry Potter and the Balance of Earth.
Order of the Phoenix, easily.
deathly hallows bc it is the last one 😊