I like how you've phrased the question. I think that there's a difference between 'favourite book' and 'favourite read': I may never reread some of my favourites (looking at you, Infinite Jest) but there are a lot of good books that I just love to read over and over. The Phantom Tollbooth is one of my favourite reads. It's written for children so it's quick and manageable, but it's also very thoughtful, and it constantly puns and plays on its own words. A lot of common phrases of speech are illustrated literally (this is as great as you'd expect). I've read the Lord of the Rings trilogy countless times as well. It's a long journey of a series, with lots of twists and sidequests, but the only time it ever loses or bores me is in the mountains at the very beginning of the Return of the King. That's a short section in three long fascinating books.
Did you ever get to see the film version of The Phantom Tollbooth? I was allowed to rent it from the video shop whenever I was off sick from school and I faked illness so much I ended up wearing out the VHS... Also - I'm actually re-reading Infinite Jest at the moment! I'm enjoying it a lot, actually. I love a big heavy tome in my hands, there's something comforting about it.
I would have to agree that there is a difference. I loved the Eragon series yet anytime I've thought about rereading them I just can't. So I figure of you are willing to reread a book it brings in many more options than just trying to pick out a single fav. I'm actually in the middle of Lord of the Rings right now and I must say they have been much much more enjoyable than the movies. Even though the movies were pretty good.