Johnny Carson was there for a few years before relocating the show to California. I did like when Tonight was in Cal and Late Night in NY because it was like you get the east coast buzz and then the west coast buzz. Now they are just in the same building
I think SNL would be the most interesting from a production standpoint. With the set changes and all they are able to pull off live in a NY highrise it is like magic happening every Saturday night. Whereas the other shows are basically what you see is what you get.
But I would be against AGT, that would be like a knockoff of the American Idol Experience.