Who's the best running back in the league?

What does it take to be the best?  Be fast, of course.  Be strong.  Be physical.  The best prospects this year look like Arian Foster, Ray Rice, Shady McCoy, Darren McFadden and DeMarco Murray.  With Murray hurt now, he isn't as good.  According to ESPN, Week 7 has Arian Foster ranked number one.  Football Guys has Chris Johnson for this week at number 1 and Arian Foster at number two.  Arian Foster has a lot of speed and a team that is 6-1 this season.  That's great for the Houston Texans.  With Foster doing well, they may make the playoffs and he may be this year's best running back.