According to at least one website it could be OSU. Obviously that assumes they have the easiest crossover games: Illinois and NU plus they don't play themselves.
Back in the good old (for us) Big 8 days KU and KState almost always allegedly had the toughest league schedules largely because they played two great teams, us and OU plus soft non-conference games. We usually had much easier schedules because we often only played one great team, OU. The cure was simple for them: Shut up about the schedule and start beating us. Now it our turn to shut up and start playing good football.
Back in the good old (for us) Big 8 days KU and KState almost always allegedly had the toughest league schedules largely because they played two great teams, us and OU plus soft non-conference games. We usually had much easier schedules because we often only played one great team, OU. The cure was simple for them: Shut up about the schedule and start beating us. Now it our turn to shut up and start playing good football.