Barry was the better runner.
Emmit could do more in that he blocked and had more power. He is one of the smartest runners I have ever seen in that he used his blocking extremely well. That said, he needed the blockers and supporting cast to achieve the stats he managed. He would have taken a severe beating in an O that provided him with the tissue thin cover that would have come with bad team, and he would have had less opportunities to be a chain moving RB.
Barry Sanders had a freakish ability to change direction without slowing down at the usual rate, and he had vision like a MFer. His stride was also unusually long for a guy his size. He could go from sprint to lope to juke to lope to sprint with two changes of direction without losing that much momentum or speed. He would have been really successful on almost any team.
Sanders over Emmit, though taking Emmit is not really a losing proposition.
Emmit was a sort of poor man's version of Payton. Both were tough, smart runners who blocked tenaciously and would catch the ball out of the backfield. Payton was also more elusive and faster.
The only thing that Payton did not have was unfair size. That is why Jim Brown remains the greatest of all time, in my opinion, as he was faster than almost everyone he played against and was bigger than most. If you put sprinter's speed into a 260 pound RB with change of direction and vision you would have a modern day JB. He was a a true freak.
1. Brown
2. Payton
3. Sanders
After those guys, who I consider the cream, you have others like Campbell, Dickerson, Simpson who were elite.
Sayers was amazing but his career was so short it is hard to know where to put him. I mean, Campbell has a similar issue, but he did not dominate quite like a Koufax, and Sayers lags behind Campbell noticably.
Smith would come just below that second tier grouping. He is the best of the Franco Harris level players. Top 10 ( and Harris might fall just out of that first dime).
That's how I see it (only one guy, Brown, played before I started watching football).