The best pure RUNNER that I ever saw was Barry. He was so good that I've seen his own OL just stop and watch him run. Crazy stuff. The stop/start, change of direction, cutting ability. Just a thing of beauty. But he also had a LOT of negative plays.
The best all-round RB that I've ever seen play was Emmitt. This man could do anything that you needed and did it well. Not the fastest (CJ2K), not the strongest (Alstott), not the most elusive (Barry), not a bulldozer (Okoye), not the best receiver (Faulk), didn't strike fear into the hearts of defender (Bo, Earl); but he could do it all at a VERY high level. And his negative plays were minimal.