Gaara is definitely scary to begin with, the way he just goes around killing everyone without even blinking an eye or showing remorse. After him, Orochimaru is definitely scary as the majority of his screentime is just wanting to get Sasuke's body for a technique he probably wouldn't be able to use xD
Orochimaru hands down. The fact that he looks like a snake and that he can't die is enough for me. When I first watched the naruto series, Orochimaru always gave me the creeps. I mean Gaara can be scary too, but he has his reasons. Orochimaru on the other hand just has his obsession of collecting data and learning every jutsu through all of his experiments which is just outright disturbing.
to be honest, to me they both don't actually seem that scary. Gaara is not a cold-hearted killer. It was basically a mask he put on thanks to his father is what I think. Orochimaru is a snake person, but I personally like reptiles.
gaara i mean orchimaru aint scary he just a creepy loser who went mad when his parents died...gaara in the beginning he wanted to kill so many people and his voice sounded like a emo who wants people to die for fun (which he wanted) now in shippuden i still think he creepy cus of his voice...