Too hard to say, each had their own team (some had good offensive lines, some had lots of other RB's in front of them, etc).
From the media guide, to help with the discussion....
Stats suggesting Alexander by a very LONG shot in my opinion.
MOST CAREER 200-YARD RUSHING PERFORMANCES
4 Bobby Humphrey
284 at Mississippi State ........................................................................................Oct. 11, 1986
220 at Penn State ..................................................................................................Sept. 12, 1987
217 at Tennessee ....................................................................................................Oct. 18, 1986
204 Auburn............................................................................................................ Nov. 29, 1986
3 Shaun Alexander
291 at LSU ................................................................................................................Nov. 8, 1996
214 at Mississippi ...................................................................................................Oct. 16, 1999
206 Vanderbilt .......................................................................................................Sept. 12, 1998
MOST 100-YARD GAMES IN A SINGLE SEASON
9 Mark Ingram ......................................................................................................................... 2009
9 Trent Richardson .................................................................................................................. 2011
7 Shaun Alexander ................................................................................................................... 1999
7 Sherman Williams ................................................................................................................. 1994
6 Kenneth Darby ..................................................................................................................... 2005
6 Shaun Alexander ................................................................................................................... 1998
6 Siran Stacy .............................................................................................................................. 1989
6 Bobby Humphrey ................................................................................................................. 1986
5 Eddie Lacy
MOST CAREER 100-YARD RUSHING PERFORMANCES
15 Shaun Alexander ..............................................................................................................1996-99
15 Bobby Humphrey ............................................................................................................1985-88
13 Trent Richardson ........................................................................................................ 2009-2011
12 Kenneth Darby ................................................................................................................2003-06
12 Sherman Williams ............................................................................................................1991-94
12 Mark Ingram ....................................................................................................................2008-10
7 Eddie Lacy
ALABAMA’S CAREER 1,000-YARD RUSHERS
Player (Years) .................................................................................................. Yards
1. Shaun Alexander (1996-99) ................................................................................................ 3,565
2. Bobby Humphrey (1985-88) ............................................................................................... 3,420
3. Kenneth Darby (2003-06) ...................................................................................................3,329
4. Mark Ingram (2008-10) ........................................................................................................ 3,261
5. Trent Richardson (2009-2011)............................................................................................. 3,130
6. Johnny Musso (1969-71) ..................................................................................................... 2,741
7. Dennis Riddle (1994-97) ..................................................................................................... 2,645
8. Bobby Marlow (1950-52) ....................................................................................................2,604
9. Johnny Davis (1974-77) ....................................................................................................... 2,519
10. Sherman Williams (1991-94) .............................................................................................. 2,486
Eddie Lacy............................................................................................................................2,402
SCORING RECORDS
POINTS
Game
30 Shaun Alexander vs. Brigham Young (5 touchdowns) ..............................Sept. 5, 1998
30 Santonio Beard vs. Mississippi (5 touchdowns) ...................................... Oct. 12, 2002
24 Bobby Marlow at Georgia Tech (4 touchdowns) ....................................Nov. 18, 1950
24 Johnny Musso at Florida (4 touchdowns) ...............................................Sept. 25, 1971
24 David Casteal at Mississippi State (4 touchdowns) ................................. Oct. 29, 1988
24 Siran Stacy vs. Memphis State (4 touchdowns) .......................................Sept. 16, 1989
24 Siran Stacy vs. Tennessee (4 touchdowns) .............................................. Oct. 21, 1989
24 Dennis Riddle vs. Kentucky (4 touchdowns) ............................................ Oct. 5, 1996
24 Shaun Alexander at LSU (4 touchdowns) .................................................Nov. 9, 1996
24 Shaun Alexander at Florida (4 touchdowns) ............................................. Oct. 2, 1999
24 Trent Richardson at Mississippi (4 touchdowns) .................................... Oct. 15, 2011
Season
144 Shaun Alexander (24 touchdowns) ........................................................................1999
144 Trent Richardson (24 touchdowns) .......................................................................2011
132 Leigh Tiffin (30 field goals, 42 PATs) ...................................................................2009
120 Mark Ingram (20 touchdowns) ..............................................................................2009
115 Jeremy Shelley (21 field goals, 52 PATs) ...............................................................2011
114 Eddie Lacy (19 touchdowns)
Career
385 Leigh Tiffin (83 field goals, 136 PATs) ........................................................... 2006-09
345 Philip Doyle (1 touchdown, 78 field goals, 105 PATs).................................... 1987-90
326 Michael Proctor (65 field goals, 131 PATs) ..................................................... 1992-95
312 Van Tiffin (59 field goals, 135 PATs).............................................................. 1983-86
300 Shaun Alexander (50 touchdowns) .................................................................. 1996-99
TOUCHDOWNS
Game
5 Shaun Alexander vs. Brigham Young (5 rushing) ......................................Sept. 5, 1998
5 Santonio Beard vs. Mississippi (5 rushing) .............................................. Oct. 12, 2002
4 Bobby Marlow at Georgia Tech (3 rushing, 1 receiving) ........................Nov. 18, 1950
4 Johnny Musso at Florida (4 rushing) ......................................................Sept. 25, 1971
4 David Casteal at Mississippi State (4 rushing) ........................................ Oct. 29, 1988
4 Siran Stacy vs. Memphis State (4 rushing) ..............................................Sept. 16, 1989
4 Siran Stacy vs. Tennessee (3 rushing, 1 receiving) ................................... Oct. 21, 1989
4 Dennis Riddle vs. Kentucky (3 rushing, 1 receiving) ................................ Oct. 5, 1996
4 Shaun Alexander at LSU (4 touchdowns) .................................................Nov. 9, 1996
4 Shaun Alexander at Florida (3 rushing, 1 receiving) ................................. Oct. 2, 1999
4 Trent Richardson at Mississippi (4 rushing) ........................................... Oct. 15, 2011
Season
24 Shaun Alexander (19 rushing, 4 receiving, 1 kickoff return) ..................................1999
24 Trent Richardson (21 rushing, 3 receiving) ...........................................................2011
20 Mark Ingram (17 rushing, 3 receiving) ..................................................................2009
19 Eddie Lacy (17 rushing, 2 receiving)
18 Siran Stacy (17 rushing, 1 receiving) ......................................................................1989
17 Shaun Alexander (13 rushing, 4 receiving) .............................................................1998
17 Bobby Humphrey (15 rushing, 2 receiving)...........................................................1986
TOUCHDOWN RESPONSIBILITY
Game
5 Santonio Beard vs. Mississippi (5 rushing) .............................................. Oct. 12, 2002
5 Shaun Alexander vs. Brigham Young (5 rushing) ......................................Sept. 5, 1998
5 Gary Hollingsworth at Mississippi (5 passing) .......................................... Oct. 7, 1989
Season
24 Shaun Alexander (19 rushing, 4 receiving 1 kickoff return) ...................................1999
24 Trent Richardson (21 rushing, 3 receiving) ...........................................................2011
23 John Parker Wilson (18 passing, 5 rushing) ...........................................................2007
22 Harry Gilmer (9 rushing, 13 passing) ....................................................................1945
21 Greg McElory (20 passing, 1 rushing) ...................................................................2010
20 Mark Ingram (17 rushing, 3 receiving) ..................................................................2009