I have not been to Norman for a game, but I have been to Ames and Lawrence. Ames gets my vote, although the Jayhawks were playing the aggies, so the crowd may not have been that into it. Also, WVU just looks like a hostile place to play.
I think everywhere but Austin, Lubbock, and Fort Worth are tough places to play. Waco is tough for the crime......
Kansas is always the best team, so, I would say KU is the hardest place to play (even if the place was just crickets chirping).