To me it was Hogan turning heel, I was totally not expecting that and was not thinking that Hogan would be heel again in his career. He was just so over with the crowds in the 80's..and still had a decent following in the 90's..though not as strong. It was a total shock when I saw that.
Bischoff being hired by Vince, though shocking was not as big as Hogan turning heel in my opinion. By the time he joined Vince, Vince had already bought WCW and ECW and it was more possible for something like Eric working for Vince to happen.
Plus, Hogan turning heel had a bigger impact in wrestling as a whole than did Bischoff working for Vince.
Hogan turning heel and joining the nWo for years he was the perfect role model for kids with his catch phrase of train, say your prayers and take your vitamins and then he comes out and tells everyone that he only did it for the money people geniuely started to hate him. The reason why Bischoff being hired by McMahon wasn't shocking to me is because it wasn't be beneath Vince McMahon to hire Eric Bischoff just to fire him in the long run so that he can say that his former competition use to work for him.