I saw Bo play. I saw Jim Brown, too. Brown was very fast and bigger than guys he played against. Bo was big, too, but not atypical of a FB or HB. He had speed that I can only describe as "don't blink or you'll miss how he ended up in the end zone." He was incredibly strong, too.
Walter Payton was the best FOOTBALL PLAYER, period. The guy rushed for 2nd most yards for his career among them all, he was regarded as an elite blocker for a RB, he was the team's backup punter, and he was 3rd string QB. When he retired, he could have put on 20 pounds and played another 5 years as an elite FB.
Steve Young gets my vote for best QB. The guy threw for 4000 yards twice and 3000 in 4 others (almost 4000 one of those). He also rushed for over 500 yards one season, and 400+ four other times. He had a great and accurate downfield arm.
Jim Kelly deserves a mention - he guided his team to the SuperBowl 4 straight years, though they lost all 4 times. Troy Aikman, too - his teams simply won as they should have, no need to come from behind.
DE - Bruce Smith.
TE - Dave Casper.
LB - Lawrence Taylor
WR - Jerry Rice
Safety - Paul Krause or Lott.
CB - Deion Sanders