As much as people slam on John Madden, he got this 100% right: Barry Sanders was the best runner of his day, Emmitt Smith was the best running back. Emmitt also had the fortune of playing for good teams.
Barry mostly played for mediocre teams (I should know as I'm a Detroit Lions fan), they only got really good once and they were definitely worse than the Redskins that year, and before the next season started the O-Line got decimated by injuries and even an off-the-field death. (Everyone knows the story of Mike Utley, but few remember that Eric Andolsek was killed gardening on his front lawn by an out of control truck during the following off-season.) Just like that, the Lions O-Line was decimated and never was that good again.
Its hard and perhaps wrong to compare a guy like Barry who carried his team to a guy like Emmitt who had the surrounding cast.
As for Rice, the guy was great. Clutch too. I've never seen anyone so good at all aspects of wide receiver... some have been better at one part... Randy Moss as a deep threat... Cris Carter at body control catching a ball on the sideline. But Rice did it all, and wide receiver is a position where its more obvious when you're being carried by great team or if you're great on your own. Rice was the latter, unequivocally, which is more than I'll say for Emmitt.