I would say all the saw movies or hostel 1 and 2 since they show everything that happens and its not pretty
my "most horror movie" is Spoorloos ,. is dutch and france talking for more scare! , u that advice me plz! the thriller movie . of ,. it has bad scene and also scary frighten , a movie is scare u!
'Let the right one in' is good - http://www.imdb.com/title/tt1139797/ 'Splinter' is not good - http://www.imdb.com/title/tt1031280/ 'Eden lake' is most horrifying - http://www.imdb.com/title/tt1020530/ 'The girl next door' is horrifying but less so than 'Eden lake' - http://www.imdb.com/title/tt0830558/ 'Hostel 2' is quite good - http://www.imdb.com/title/tt0498353/ 'Mirrors' is ok - http://www.imdb.com/title/tt0790686/ Those are all the horror movies I've seen recently.
And I wonder at the audience of SAW series I mean it's so inhuman.. Horror things and SAW stuff are altogether different.. (Horror means something paranormal and SAW is totally ABNORMAL and kinda in-human psycho butchers stuff Mirrors was okay and The Ring was fine as an answer to OP.