My favorite book is the Sorcerer's Stone. It brings back so much nostalgia from when I was little and read it the first time and all the different points in my life where I have reread the series. I love the character building as well. It really sets the tone for the series as a whole. I still feel joy and excitement each time Harry lays on the floor in the cabin on the rocks counting down to his 11th birthday as Hagrid is about to knock the door off its hinges.