J.K. Rowling. Her books are something that just could never be matched. They are so complex and well-planned, not to mention well written, with humor, morals, action, love, and just a deeper meaning to them. She took the whole good vs. evil to a whole new level. They are books that anyone can enjoy, young or old, that you never tire of reading them.
M.P.O. is okay but honestly all of her books are pretty much the same. Just a different time period and mission but otherwise once you read a few, the rest just aren't exciting, plus they are at such a low level, that no one over nine or so could actually enjoy them. Sure parents may think there cute but other than that they are so dumbed down. I liked them when i was 8 but i've never picked up a book since.