That's hard to say, because a lot of horror games' level of fright is down to my age at the time. Like, the Jurassic Park Genesis game got me to hide behind the bed in the T-Rex section. Years later, Blue Stinger gave me nightmares. The former isn't a horror game, and the latter, while TECHNICALLY survival horror, is bereft of fear factor with the benefit of age. Also, fear factor inevitably declines with subsequent playthroughs - RE2 for instance, that was already in decline with the B scenario.
Whatever. You've already played numerous RE games, so I'm going to throw Dead Space in there, because yes, it's scary at least the first time round. Also, stay away from Alien: Isolation. Sure, the xenomorph might get you to crap your pants, but I'm already at the point where my reaction to the creature isn't "oh God oh God oh God" but more "just fuck off already!" The weaponless section in Colonial Marines is more scary than anything Isolation has thrown at me so far.
(Yes, I really dislike Isolation, how could you tell?)