I'd pick Robby Denning. Deer hunting will always be my favorite and I feel like muleys are where I have the most to learn. I'm a rifle hunter and don't know what other rifle hunter I could learn more from.
Couple guys mentioned Fred Bear.
My buddy Chuck has hunted with him on his ranch when he was a rep in the hunting fishing biz many years ago. Being a fellow Lefty Fred actually gave him one of his bows.
He said Fred was a great story teller....but you wouldn't actually want to hunt side by side with Fred....he wasn't the kind of guy to say, "go ahead, You shoot"