Harry Potter 30 Day Challenge!
Day 1: Your favourite of the 7 books

Harry Potter and the Half-Blood Prince. I feel like this book is a really big turning-point for the series. It introduces what essentially becomes the final plotline, the horcruxes, and it gives us more insight into Tom Riddle/Voldemort as a person. You kind of come to understand how he came to be what he became. Aside from that, Draco Malfoy gets some serious character development, as well. You see his struggle and his fear. He becomes more than just the stuck-up asshat that Harry hates. He really is a tragic character, and you get to see that here for the first time. This book really highlights the idea that the world isn’t separated into black and white, good or bad, even if Harry doesn’t really see it at first.
Also, it’s real cool.