Having 'done' flippant (and uncovered a can of worms in the process), perhaps it's my turn to 'do' serious.
Problem is, I really can't choose! I'm not really well-read, but I suppose I have got through a lot of books in my lifetime!
LOTR: after first ploughing through it as a teen, probably the one I re-read the most number of times. Loved delving deeper into it picking out more detail. And I can quote a lot of it verbatim. Very good prose but by no means my best read: indeed the last part somewhat drags. And too much of a cult subject, I don't really go for cults.
Dickens? No. I recall vividly reading out the entire David Copperfield to my lad when he was still (age about 7) to young to read it but old enough to take it in. It was worth it just to hear his squeals of delight each time I assumed the 'Micawber' voice. But I don't like Dickens' plot lines.
Moby Dick I think it's probably my favourite read - and one of the funniest - for the first dozen chapters or so. After that it drags intolerably. They should stay on dry land. I never finished the book. But it was worth mentioning.
OK: more modern. I think The Constant Gardener is one of the best-written I've come across, superb characterization and plot, and writing style. But so depressing, so much the opposite of 'feelgood', I can't really stomach it.
Decline and Fall (Evelyn Waugh) Hilarious and superb ending, but the racist episodes preclude it. Of course it was written for a different age.
So: I've nominated a few runners up, but no champion yet. Keep thinking.