Sanders jigged around behind the line looking for openings (and frequently getting tackled behind the line in the process) too much. No runner afraid to run to darkness could ever be the best ever.
When you have no offensive line and 11 men are running after you, let's see how well any other running back would do in that situation. Sanders was alone on that field against 11 guys and he could not be stopped.
BTW, just about all of the NFL greats, when asked, will say Sanders without even thinking about it. It's documented on film.
That is why it is my firm belief that Adrian Peterson WILL be the best running back EVER to play the game. There, I said it. He has everything: speed, balance, power, doesn't fumble, hits the hole hard. HE WILL BE THE BEST EVER.