I voted for Harry Potter because I enjoyed those books, but I would give a close 2nd to the Earthsea series for originality. You don't read those books and think "oh, disguised Middle-earth again." They have some nice philosophy underlying them, but they're also brooding, and I get the sense reading them that no one in Earthsea is ever happy and never will be, or if they are enjoying life, they'll keep it a tight secret, so it's not a place I really want to visit. Middle-earth had plenty of tragedy and melancholy Elves, but there was plenty of joy to offset that, making it seem a place you'd want to revisit.