For me, hmmm... hard to say. I like a lot of books. Especially Science Fiction and Mythology. But my favorite would be... Harry Potter. Or, The Lightning Thief.
The Monster Blood Tattoo series, that being the first book, the second Lamplighter, the third Factotum, my favorite. It's probably the best fantasy series you'll ever see. He's been working on the world for at least ten years to twenty, since he was eighteen or so. You gotta read it. The second you do, you'll be captivated.
I enjoyed Sabriel quiet a bit. But my favorite books are the Drizzt Do'Urden prequels! Gotta love Guen.
Percy Jacksom series Hunger Games trilogy Warriors (cats) series [It sounds lame but it actually has a pretty good plot.. Up until the 3rd arc of books -_-] Flawed Dogs Monster High series A Dog's Life
Divergent~I couldn't put it down, set a new personal record of 1 hour 30 minutes to finish a book. (Around 700 pages, I think. Somewhere in that range)