I have to go with Dead Space 1 because I enjoyed it the most. The story was intriguing and the gameplay superb. It also was the scariest one. I liked that it had the something new factor and they tried something interesting with the narrative.
Its a kinda survival horror game from Konami. You discover underground society under the Tokyo subway and mutating monster is chasing you. You can only run and hide plus you can find partners like little schoolgirl.