I feel like the people who ask that question usually mean well and want to get to know me a little better, but they're just really asking the wrong question. Having to narrow down everything I've ever read in my entire life into one book that will supposedly define what sort of person I am to the random professor or person at a cocktail party who doesn't even know me is just unfair. And what I respond with inevitably makes me sound shallow, ill-read, or like I'm trying too hard to be pretentious. And while I am silly, I don't think I'm shallow, I'm definitely not ill-read, and trying to appear to be pretentious is just like, way too much work for me and I'll inevitably blow it when I make an unintentionally off-color joke.
So I hate being asked what my favorite book is.
I get that the whole idea behind asking that question is that people want something succinct and concrete about you. But saying that I have short hair or I am sarcastic or that I am of medium height is something completely and totally different from telling you that I think I could and would live happily in the world of Harry Potter for the rest of my life, Tamora Pierce's Tortall fantasies are my comfort reads, I read Rebecca by Daphne DuMaurier every fall since it first haunted me for over eight years ago, I think that Jane Eyre is possibly the coolest heroine ever, John Green always makes me laugh and laugh and cry, Jennifer Donnelly's historical fiction is so beautiful I want to cry, and that there are hundreds of books whose titles I have written down in a tiny striped notebook that I've read and loved equally and unequally, but they're not for everyone--they're only for me.
It's not the same thing at all.
But I just smile and say, "Rebecca by Daphne DuMaurier." And then let them think what they may.