I haven't seen Ju-On or Ringu, so I can't comment on which is the better adaptation. That said, I enjoyed The Ring a whole lot more. The Grudge was scarier for me, personally, but I like my horror to be more suspenseful, rather than all out pee-in-your-pants-and-scream-like-a-small girl scary. The Grudge isn't the freakiest move I've ever seen, but I'm a wuss, and The Ring did a lot better job at entertaining me.