They all have their scary moments. RE1 and the "poptart" Crimson Heads, RE2 with the magic mirror Licker, RE3 with Nemesis, CV with those damn naked weinerless zombies, RE4 with the Regenerators, RE5 with the... nevermind.
I find REmake to be the scariest. I just love the whole mansion thing. Mansions have always creeped me out ever since I watched my dad play RE1 all those years ago on the PlayStation. The atmosphere can be nerve-racking for a 4 year old. Hell it STILL freaks me out when I'm 18!