Naive on your part to attempt to compare eras with different circumstances. All we can do is hypothesize. Given today's training techniques, diet, nutrition who knows what Jim Brown could do for certain he had the size, speed and tenacity of AD. All you can compare is how they did against the best in the game when they played the game. Thus we all only have uninformed opinions that reflect personal bias. No question AD has the opportunity to contend for the best RB that ever played the game but he is not there yet. He still needs a few more years, a good offensive line and good health.
AD needs to rush for 2,000 yards in 2013 and 2014 to move to number 8 on the all time rushing list behind ****erson and rush for 2000 yards per year for almost five season (9,506 yards) to catch Emmitt Smith's all time record. Presently AD is not in the top 32 in all time career rushing numbers.
Lets allow AD to have those five seasons to confirm he ranks where many of us think he could rank.
http://en.wikipedia.org/wiki/List_of..._yards_leaders