This is kind of moot, truthfully I'd go, now (or look first at, but they're both getting praise so...) for Chris Bishop or Ethem Alpaydin's new books. But between Norvig and Mitchell, Norvig has 138 pages on learning vs Mitchell's ~390, but, Mitchell's is from a different era, Norvig is easier to read - larger pages, more diagrams, better writing, and you know where you are better - and fresher material. To each his own. But like I say, I'd probably go with one of the even newer ones. For a while Mitchell was all there was, then Norvig came along, and now there're a few to choose from.