The similarity is that Rowling was most certainly influnced by the Narnia books, as was anyone who wrote fantasy for teenagers, from a charecter point of view there's not much to compare the two, if anything he's similiar to the boys from the Pevensie family, who - like him are regular teenagers transported into a magical world where they are heroes, very different than their usual, mundane lives.
Better? I'll stick with the original, Narnia and the rest of the series, though the Potter films are much better than the Narnia franchise.