I think that 3rd person tends to emphasize the player's sense of vulnerability via the visible exposure of the player character, whereas 1st person emphasizes the sense of viscerality by situating the player as the direct recipient of attacks. 3rd person horror = exposure, 1st person horror = enclosure. Each perspective has its respective strengths, but given that 'horror' tends to encompass a range of emotions, it's hard to say any one is better than the other.