Most horror movies have bad guys in the form of normal-looking human beings, mutated sub-human freaks, or some variation in between.
Some people are more afraid of the unassuming, friendly-looking guy who lives next door type who turns out to be the bad guy in books and film. One minute he could be mowing the lawn, waving at neighbors, then the next, he could be slicing and dicing in his basement. It’s a shock when you’re not expecting it.
While other folks prefer the in-your-face evil that jumps out at you. Both can be scary if utilized properly. Above all, they need to be convincingly scary, no matter how they’re presented.
I choose both, depending on how it’s executed. But I still have a special place in my heart for the overt monsters. 🙂