Which book has left the biggest impression on you?
Oh goodness, there's quite a bit that fit the bill, to be perfectly honest. Some of which I have already mentioned previously. If I have to choose, I'd say it's probably a three-way tie between To Kill A Mockingbird by Harper Lee, Flowers in the Attic by V.C. Andrews and Out by Natsuo Kirino. All three left a big impression on me for different reasons and at different points in my life.