I would pick either Michael Jordan or Lebron James.
I know there are some that dislike Lebron, but I have never seen an athlete that size be able to do the things he can do. It might be difficult to listen to him for a long time, but watching him play amazes me. I know he just plays basketball, but he is still one of the greatest "athletes" I have ever seen.
Willie Mays was my favorite player and IMO the greatest all around player ever. I could watch highlights of him for hours. Not sure about 8 hours though.
Football highlights, Aaron Rodgers or maybe Barry Saunders.
And I actually have watched 8 hours straight of Cassius Clay, and then Mohammad Ali.