It’s probably a cliche answer, but the only book that springs to mind is the Bible.
As a Christian, the Bible is the Word of God, the foundation of my faith. It’s more than a favourite book: it’s essential.
No, I’m not always as “religious” or dedicated about reading it as I should be, but that doesn’t detract from its importance.
So I’ll move onto the logical associated question: which version of the Bible is my favourite?
I’ve read several over the years – the King James Version, the New King James Version, a replica of the original 1604 King James Bible (which, frankly, is unreadable). I’ve read the Good News, The Message, the Contemporary English Version, the New American Standard Version.
All have advantages and disadvantages, but my favourite is the New International Version for its balance between ease of reading and conceptual depth.