I like many books, and can't really choose one as a favourite as I have a favourite from every genre.
But, my favorite fiction book/novel is probably And then there were none... by Agatha Christie.
I had to read an Agatha Christie book for school a few years back, and I chose this one because it stood out.
It is about a series of murders commited on an island, but, as opposed to other Agathas Christie's books, there isn't a detective to save the day and investigate.
The 10 people just have to stay on this island and watch each of them killed off, one by one. This isn't really a detective, it's more of a pshyological thriller.
It is my favourite novel because it made me start reading more again, and also, when I reread it this summer, I started really enjoying novels more oriented to psychology and philosophy. That's why I am reading Crime and Punishment now, which might be my new favourite book when I finish reading