Second-biggest. The Patriots were 14-point underdogs that year. But the Jets were 18-point underdogs when they won SB III.
True...but remember that John Unitas didn't start in that game. I don't consider that all of an upset, especially in the era where the QB called his own plays. Also remembering the low opinion of the AFL at the time, I think the betting line was skewed a bit.
Although in terms of press predictions, the two games were probably on par...no one was picking either of them.