In my opinion, it's both the best YA series ever and the best कल्पना series ever. Why? Harry Potter is the best of everything - the best characters, the best plots, the best writing.
The characters are people आप can fall in प्यार with, and not just the main हीरोस and the main villains. Even और minor characters are pretty extensively developed, like Snape, Pettigrew, Neville, even Dean या 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.