Who is better, introduction or Sadako? I have seen this film.

Introduction VS Sadako, that's a bad movie. There is nothing to say, it is not authoritative at all. But one thing can be proved, ghosts and ghosts only have a draw, and there is no victory or defeat. Because ghosts are dead and can't be killed. Sadako is like an authority to Kayako. Nobody killed anyone, but in the end it was just a merger.