Oro was butthurt because he could not become the hokage and had a grudge against the third and the village and so he took his revenge, other than that he was always focused on his experiments towards obtaining immortality and other shit without caring about the means he employed to do them.
Danzo on the other hand also wanted to be Hokage and loved the village. But the methods he used to achieve his goals or missions were too twisted and cruel and ****ed up a lot of people like Nagato, Kabuto, Itachi, Sasuke and the entire uchiha clan leading to almost half the problems in NV. So in Danzo is more evil indirectly imo.