As some of you mentioned earlier "IT" was really scary. The thing that made it scary was the clown could appear at anytime to get you. I haven't seen the first movie of "The Ring" but I saw the 2nd one, it was scary too, not the director's cut that was just long and boring. The other version was fast and the thing got people really fast and again with magically appearing to get people.
The Grudge is the only one of them I actually saw in theaters but it wasn't as scary as the other ones. Scary thing mostly stuck to that one house so it didn't appear out of nowhere to get people that much. Of course I only saw the American version of The Ring and The Grudge so I don't know, the Japanese versions (originals) might be scarier. Chucky from Child's Play was more disgusting then scary for me.