That would be Conte
Imagine having the current stadium with a manager like delneri ! This stadium affect would be useless.
It's hard to compare, but I think the Stadium is more important because it affected the institution status. As I said, the supporters seemed to care again, to be excited again. It's a whole new atmosphere.
But I'm sure that if you are talking about the people, considering the players brought and Conte, I have no doubt that Conte is the most important of them all.
The funny thing is that during pre season he always used the so called 424, using even Marchisio as a left winger and it didn't seem to work out... everybody was hoping that he would open his eyes to the 433, and he did.
Another major factor is the physical condition of these players (and also the lack of European games). They all run like hell, from beginning to the end. IMO it's the marking scheme which comes closest to Real Madrid and Barcelona pressing marking, really great.