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.