The best player I ever got watch for the Broncos was Joe Sakic. What a treat it was every night you got to watch this young guy perform. Then when Moose Jaw came to town it was the Sakic and Fleury show. It was simply awesome!!
I never got to see him play as a Bronco, because I wasn't around, but Bryan Trottier would probally have to be right up there as well.
There's a long list of past Broncos that have made it to the big's, but these two, in my opinion, would probally be the best.