Cackling is the most obvious. Sure, you'll have scientists in the lab, and some will probably be genuinely mad, but sociopathic rather than the cackling maniacs. Cold, clean labs where they work in silence, having muffled any screams, and with arrangements to have the blood washed neatly away. The mad scientist is a lot more personal about it. And of course though it will be rife with assistants and other employees, there will not be a mad scientist's beautiful daughter; putting her there would be nepotism, and not an impersonal corporation in action. Besides, they would have their lives neatly divided.
The corporation would be more vulnerable in some respects. Sure, you could probably make the HQ as hard to attack as the mad scientist's lab in the castle, but it would take more work, and you would have to plump it down in the city, or at least suburbia. Howling wilderness and mountain tops are right out. They have assets and charters to forfeit.
On the other hand, they have more powers, too. The mad scientist could drop the portcullis and head for the hills. The corporation could have the torch and pitchfork wielding mob arrested and hauled off to jail and charged with numerous offenses. Probably convicted too.
