Ranking installments of everyone's favorite transphobic white angloid attempt at writing shonen with antisemitic undertones because my 50 y.o. mom is a Rickman/Snape fan and forces our entire family to rewatch all of the movies each holiday season.
Worst - Prisoner of Azkaban. Really unpopular opinion, but I feel this is the messiest out of the early books, with a generic "believe in yourself to deafeat a monster (dementor)" shonen message told with the help of the atrocious time travel subplot (JKR's worst mistake besides, y'know, becaming a far-right grifter) and untolerable for me at least amount of quidditch padding.
5th place - Half-Blood Prince and Deathly Hallows (ranked as one book because HBP is just a set-up for DH's story, it would have pretty much zero literary value as a standalone book) A dissapointing end to the series. Voldermort fully turns into a cartoon villain and stops being a credible threeat to any minimally adult reader (despite showing signs of being capable of more in GoF and OoF). Also I hate how Voldemort invokes Hitler symbolism despite, if anything, having more in common with Grand Wizard (pun intended) of the Klan. The story becames irredeemably reactionary, with Voldemort being defeated by the mystical "power of love", Dumbledore being venerated as a saint by the narrative (despite there being a fucking perfect set-up to make him a "second main villain"), Hermione accepting the naturality of the House Elves' slavery and Harry becaming a wizarding cop treated as a happy ending.
4th place - Philosopher's Stone. I know it was intended as purely children's book originally, but it still looks intolerably cartoony and cheesy compared to the later parts.