I am not sure - but if you want to decide which Harry Potter book to buy, please note that the Harry Potter books form a continuous story, so you are best off if you read them in order.
harry potter
Goosebumps is the second best-selling book series under Harry Potter.
Harry Potter
harry potter
The best selling book in all countries would be "Harry Potter and the Deathly Hallows" because it is the latest one and people are thriving to bookstores just to get the book.
harry potter
Harry Potter.
probably the deathly hallows
They started with selling a few products in Harry Potter and the Order of the Phoenix, but the real shop started in Harry Potter and the Half-Blood Prince.
No, that was Harry Potter and the Sorcerer's Stone which was released in June 1998. Harry Potter and the Chamber of Secrets was not released in the US until 1999.
twilight saga and harry potter series
The lastest (and last) Harry Potter book is Harry Potter and the Deathly Hallows. It was published in 2007.