It is pretty simple to say super human strength and call it a day. In a sport, especially one like football, strength is going to win most of the time. Speed is pretty helpful, too, but enough guys can prevent a fast person. With super human strength, though, you can just hand the ball off each down and let him run it basically into the end zone each time. Even if you aren't quite strong enough to drag eleven guys, you will still have the help of the rest of the team to block for you and get you into a mismatch. The same could be said for speed of course, but strength somehow seems like the better power for an individual. Insane speed would set up the rest of the team to make plays, but strength means your player is always the one you want the ball to go to. There are a lot of good options, but super human strength is hard to top.
Thank you to @enigmatic, @Kyamprac, @mithrandir, @Mooty99, and @Number 82 for some of the sigs in this rotator.