Sixth Sense is clearly the film with the most general appeal and it is really wonderful. That said, I think Unbreakable is his most compelling and best script. Split is also pretty good, thanks to McAvoy's amazing acting performance. Someone else could have made that role into a real mess.
Signs and The Village are watchable and are decent semi-horror fun that each fall apart in a really, really big way in the final third.
The Lady in the Water, The Happening, The Last Airbender, and After Earth are pretty much unwatchable. They make no sense and feature scripts that contain multiple, "well that is just the stupidest thing ever!" moments.
I did not see The Visit, but a lot of folks say it was a pretty good horror kinda film.
Here is a chart I built a while back when I had high hopes that Glass would be good:
https://pbs.twimg.com/media/DpVMNd0XgAAdfXg.jpg:large