My father and I had a long conversation based on a long conversation on a national radio show that we both thought was weak.

Who do you think was the greatest running back of all time?

College
NFL

Separate or inclusive.

I pick Jim Brown for all time and Hersheal Walker for best college runner.

Many,  many runner ups such as many from USC and TEXAS which is why I thought of this question.

I Would Pick

Barry Sanders: Pro
Tony Dorsett: College

I'll answer that the day I can pee standing up without it running down my leg.

College: Orinthal
Pro: Gale Sayers

Bo Jackson would have been only if he had not gotten injured so early in his career.
No particular order

Sweetness/Walter Payton
Jim Brown
Franko Harris
Earl Campbell
Barry Sanders
Hate him but gotta mention the juice OJ Simpson

Sorry, but Walter Payton has to be in contention.

Pro: Jim Brown, with Payton and Sayres in close contention.
College: You-know-who. Damnit anyway.

Pro: Jim Brown / Barry Sanders. Take your pick - bear in mind they played in extremely different eras. It was way rougher when Jim Brown played, face-masking was legal too. When Barry played you have bigger, faster, stronger defensive players. 

College: Who the f*ck really cares... ?

If you want to talk potential...Sayers and Bo Jackson.  Both injured both looked like they could be the best running backs EVER. 

Full career wise...well:  Walter Payton and Barry Sanders come to mind. 

Honorable mention to Jerome Bettis.  He may not be the best but he has been the most consistent Back I have ever seen.  Berry and Walter had a few off years.

my fav in the NFL was the Nigerian Nightmare.. Christian Okoye.. sheer power

but Barry Sanders was the best I ever saw

College I liked Jamal Lewis at UT

but Bo was unreal as well!!

I stick with my first choices. 

Though many great additions.

I actually do not know much about Gail Sayers except for a few game films and the movie.
I would put him in the same category of Bo Jackson.
I watched the last game of Bo and wow.   Just wow.
He was everything that year.  Averaging near 8 yards a carry.
that whole year was greatness.   He was in a zone.
It was sad to see him hurt.

I am no stats geek but my father mentioned a running back from the 40's as having the highest rushing average.

He ran for Army.  though my father feels that he gained benifit from most good players being busy.

I did love and I do mean Love O.J simpson.   that day was one of the saddest in my life.
OJ was a great college player and then ignored by his first pro coach.   Then succeded.
A success story until the obvious.   But still not as good as Jim Brown.  P.S.  Orinthal James is OJ real name.

Also maybe not a running back and will have to check with dad but there was a player who was very famous for dragging many players and still moving.   Running back/tight end when playing.

Due to being on the east coast and the teams the Lions had,  I did not see Barry Sanders all that much.  But I think from the few films I have seen that he was better that OJ or Walter Payton, or Harris.

Dorsett was great for the explosiveness.   I was always a Cowboys fan from an early age when my father was  a fan of Bob Hayes.

the person who gave the well thought out view of the differences between the toughness of old compared to the size of today is wise.

Anyway cool to take  a break and appreciate great achievements once in while.