Blimey, Botty, ask me an easy one why don't ya?
Hmm.
Well, I have twice nominated a certain book for "My favourite ever"/"best novel ever" - the former in a poll at my library here in NJ, the latter in the BBC poll a few years ago.
But that's probably not the same thing as "the greatest", which I think would have to be something more influential, either in that more people had read it or that it had influenced writers or people of influence.
Then you widen my choice by not excluding non-fiction and including both comics and pop-ups (I'm honest, I call em comics).
I do have a lovely pop-up Camelot. And narrow it be removing Twain, much Conan Doyle, all Malory, Fielding, RL Stevenson nd Defoe.
I assume that roleplay books are also possible nominees, making my own roleplay game a possible...(copies still available)
While I'm pondering, let me tell you what was my favourite, etc.:
It was The Cream of the Jest by James Branch Cabell.
Cabell is an incredible author, though I have to say that I'd start with a few of his other books and lead up to this one - it is, as the title suggests, a crowning moment - in a huge collection of stories which stetches over centuries and locations both real, invented, and mythical. Each book can be read on its own, but every time you rad one you feel compelled to go back and read all the otheres since they intermesh in a bewildering and mesmerising fashion. You are unlikely to encounter any of his books which don't fit into the Life of Manuel the Redeemer. He wrote about 50 books altogether, half of which at least are a part of this cycle.
Hmm.
Given all of the above musings (influence, readability, people have heard of it), I think the greatest must-read of the 20th/21st century has to be 1984.
