Hulk or the X-Men are the most feared. I'm leaning towards the X-Men. Hulk is like monsters from urban legends, where people fear them but think it's "cool" to see them. The X-Men are genuinely feared by a lot of people.
I don't think it's Spider-Man, though. I think Spider-Man has the reputation of a 60s activist. Young people love him, old people don't. People in the media hate him, those from blue-collar communities tend to like him. People outside New York hate him because they know nothing about him, but a lot in New York interacted with him and like him.