In my opinion, it's both the best YA series ever and the best ফ্যান্টাসি series ever. Why? Harry Potter is the best of everything - the best characters, the best plots, the best writing.
The characters are people আপনি can fall in প্রণয় with, and not just the main নায়ক and the main villains. Even আরো minor characters are pretty extensively developed, like Snape, Pettigrew, Neville, even Dean অথবা Seamus. They all have histories and quirks and unique personalities and very few authors are able to so vividly create such a huge cast of characters.