The 71 Nebraska team gets my vote.
We had been kicking tail that year, with the new wishbone offense, and got to the orange bowl (if I remember correctly) and they beat the brakes off of us. 38-6. It was a rude awakening to say the least. Johnny Rogers went on to win the Heisman trophy. So Cal was an extremely good team in 1970 when they came to Birmingham and beat us 42-21, which was part of the reason that the Bear installed the wishbone during the next off-season, but that '71 Nebraska team was something else.