Delany confirmed in his press conference today that in determining divisions, the relevant time period for studying competitive balance would be 1993 to the present.  With that in mind, here are the stats for that time period, courtesy of Stassen:

Winning Percentage

2 Ohio State 0.79673

5 Nebraska 0.76037

11 Penn State 0.70335

14 Michigan 0.69524

15 Wisconsin 0.68692

36 Iowa 0.58010 119

55 Purdue 0.51951

66 Michigan State 0.49512

73 Northwestern 0.48030

80 Minnesota 0.45320

96 Illinois 0.38325

101 Indiana 0.35385

Conference Winning Percentage

Ohio State 0.783

Michigan 0.691

Penn State 0.632

Wisconsin 0.592

Iowa 0.526

Purdue 0.474

Michigan State 0.467

Northwestern 0.434

Illinois 0.335

Minnesota 0.324

Indiana 0.243