Chick 1 says:

Based on the sixth book in the series, Half-Blood Prince is my favorite.  We get loads of info on Voldemort thanks to Dumbledore and his cabinet full of memories and Harry finally gets a clue about who his true love is.

The Basics: When Harry returns to Hogwarts for his sixth year, Dumbledore begins to train him in earnest for a final showdown with Voldemort and gives him an important mission concerning the new Potions Master.  Conveniently, Harry is acing Potions class with the help of a mysterious but ominous textbook.  Read more