Magic or Larry might get the nod over Jordan. The Lakers/Celtics battles of the 80s were stuff of legend. The Detroit Bad Boys could be in there as well. Jordan took a great product and made it even better, but the NBA really developed a better strategy to market itself concurrently with his era. One could even go back as far as Wilt Chamberlain, I suppose. EDIT - I typed this before reading Art's reply, but they go well together.
Who would be that guy in Football? Joe Namath, with his legendary upset prediction? There are so many guys who made the NFL great it would be hard to pin it on just one. Guys like Jim Brown or Dan Marino come to mind. Jerry Rice, Joe Montana, Walter Payton, Barry Sanders... there are good arguments for all of them and more.
Keep wreves in General Talk in 2011!