This is a very difficult one. Most books that I have loved over my reading life I still love but for different reasons. Take for instance, the Mary Stewart thrillers. The Moonspinners, The Gabriel Hounds, Nine Coaches Waiting, My Brother, Michael etc... These were some of my favourite books back when I was a young teenager, they introduced me to the world of romance and suspense. I graduated to them from Trixie Belden and Nancy Drew. They were exciting and new and romantic and I loved them to bits.
Today all of these novels are very dated and the heroines anything but modern, but I still love them for their snapshot of a time period and for the nostalgia of where I was in my reading life and the doors they opened for me. The Moonspinners is still one of my favourite books and I still love Mary Stewart.
So I used to love them as only a 14 year old girl can love books and today, 40+ years later, I love them for what they did for that 14 year-old and for the warm, cozy feeling they give me.