Here goes nothing. (Ratings 1-10.)
- Zombies: Zombies have a lot of scary potential to me because they are so often something that man made. Chemical zombies are caused by a spill at the nuclear plant or a virus spread by well-meaning but failing medical professionals or vindictive biogeniuses. They don’t just spring out of nowhere, and they once were us. Your next-door neighbor can get infected and become a zombie. Your child can get infected and become a zombie. And zombies are mindless killers. There is no rationalizing with them. There is no “hey man, we were friends once, have a little sympathy” or even “I’m gonna get you, I swear, you’d better run.” There’s just you being devoured or them being shot in the head. Also, zombies can be messy. You can make funny zombies easily, but even then they’re pretty yicky. And killing a zombie is really no more than aim and not getting killed yourself.
Favorite fictions: The Walking Dead, Planet Terror, Shaun of the Dead, Pride and Prejudice and Zombies, Breathers. Dawn of the Dead is a classic but I’ve never seen it. I’ve seen so many of the crappy zombie movies out there, but hey. Firefly‘s Reavers are sort of space zombies. The Butchers and dumbshows of Dollhouse‘s Epitaphverse are sort of zombies sans bloody pus. Braindead but still human-looking.
Scariness rating: 8 - Robots: Robots are not included in every “monster” list, but as mentioned before I do include these suckers. Robots are also something that man made, but more often they decide that they want to control us and not be controlled by us. And bad happens. They’re like us, but they don’t have our human failings: they don’t have emotion to contend with, or bodily needs (food, sleep, sex, etc.), or attachment. They can just go out there and achieve their goals. Probably pretty well, depending on their interface. Killing these guys is trickier and at times more specialized
Favorite fictions: the Terminator franchise (which I haven’t seen all of, but what I have seen… the ultimate robot quandary), Robopocalypse, Android Karenina. A lot of older robot stuff is too campy to be freaky. (Like Robot Apocalypse. Not at all scary. Hilarious and bad, but.)
Scariness rating: 7 - Vampires: Vampires also once were us. They’re strong, they’re logical, they’re capable of strategizing, they’ve got a (usually insatiable, occasionally lame) blood lust. But they can be reasoned with. Not every vampire is going to kill every human. Some are only going to kill when they’re hungry. Some like to make it a game of sorts. Some can be talked down from a murder. Some can even fall in love. Vampires are really sort of humans but with fangs (and strength and speed and whatever, depending on the mythos). Vampires are our dark side, but they aren’t pure darkness, usually. And sometimes they’re honestly pretty sexy, at least in certain media. They’re interesting, they’re adaptable. They aren’t always vicious. And the blindly bloodlusty ones are usually the easiest to kill, because they’re not using the logical human parts of their brains, they’re just powerdrunk. Normal human-killing things like guns won’t work on them unless you’ve got wooden (and sometimes silver) bullets, but it’s not hard to break a stick off a tree and jab it through, if you’re fast.
Favorite fiction: Buffy the Vampire Slayer, True Blood, Interview With a Vampire, Jane Slayre. 30 Days of Night is a good indication of a more zombielike vampire, but it’s not my personal favorite.
Scariness rating: Anywhere from 4-9. - Werewolves: Werewolves are often found where other supes are, and strictly werewolf stories are usually either cult-classic or bad. Werewolves aren’t so scary since they’re just people that are killer beasts 3 days of the month (or whenever they want, depending), and most of them can either control it or just don’t let themselves get angsty about it. And if they do they’re not worth paying attention to. The bloodlustiest ones are rare.
Favorite fiction: Buffy the Vampire Slayer, True Blood. I’ve heard of this movie called Ginger Snaps that’s pretty culty-good for werewolf stuff, but I’ve never seen it.
Scariness rating: 5. - Killer animals: Black Sheep and Supergator and Piranha. Enough said.
Scariness rating: 3. - Miscellaneous supernatural humans: Again, they’re just people. People with magical powers. Sometimes they’re like Carrie, which I’ve never seen, but I’ve heard a million references to; sometimes they’re like the X-Men, and not scary at all unless they’re evil. They’re just around. They might use their powers for evil, they might not. A lot of slasher films have supernatural elements tossed in, but they’re not always well-explained.
Favorite fiction: There are honestly too many variants to try and list a few overall.
Scariness rating: 0-10. It really depends. - Ghosts: Nowadays, they aren’t too scary. Most ghost films are more creepy than scary, and even that’s a stretch. Take for instance the Nicole Kidman film The Others. Or The Sixth Sense. Or… seriously, anything with ghosts.
Scariness rating: Usually about 2. Occasionally more. - Monsters: Animallike creatures with little or no basis in reality. Sea monsters count, yes. Demons also.
Favorite fiction: Buffy the Vampire Slayer, Sense and Sensibility and Sea Monsters.
Scariness rating: Given the camp factor, 3-5. - Witches: They aren’t all evil anymore. Mine is the generation of Sabrina the Teenage Witch, of Buffy and Charmed, of Harry Potter, things like that. Where the witches are really just people with magical powers. Some of them are evil, yeah, but most aren’t. Most are just people. Most just wanna do their magical thing. Sometimes you have True Blood Marnie, but she’s not evil because she’s a witch. She’s evil because she’s overcompensating for social deficiencies and an inferiority complex, and she just happens to be a witch at the same time.
Favorite fiction: See above.
Scariness rating: Usually around 2. Some witches can get seriously scary (Voldemort and some of the Death Eaters, like Bellatrix, are closer to 8; Hermione can be like a good scary around 7. Dark Willow is about a 9, because damn, girl, flaying? Freaky) but as a whole they’re not that freaky. - Sociopaths: Not all sociopaths are evil. Not all sociopaths are scary. But the ones that are, really are. The scariest killers are the plain old (sometimes technologically enhanced, Alpha) people who go on a killing spree. Period.
Favorite fiction: Everything ever, man. I’m a morbid nutcase, almost all of my favorite fiction is about sociopaths in one way or another.
Scariness rating: 6-10.
–your fangirl heroine.

Personally, i think zombies/vamps/wolves have been overdone in films and games to a point where it has lost its scare factor in general.
To me, the scariest would be sociopaths. People like freddy krueger, jason vorhess and those nut slashers creates more insecurity as they can be real in one way or another.
On a side note, i like dollhouse too. I dont understand why they had to end it after season 2.