The best book I've ever read was Harry Potter and the Sorcerers Stone, the first book in the Harry Potter series. I really liked it because since it's the first book in the series, I was just getting introduced to all the characters and to what was going on. If the 5th one would have been the first one, it would have been my favorite, too. Of course, I like all of the books a ton.
The basic layout of the story is: Harry lives with his aunt and uncle, not knowing he's a wizard. He finds out, goes to Hogwarts, and learns all about his past. Then, Voldemort tries to steal the Sorcerers Stone so that he can return to power and kill Harry. Harry has to stop him. The book just hooked me on the very first page, and I didn't put it down until I was finished. I did that with all of the books.