First choice: '96 Big 12 Champ. vs Texas, for obvious reasons. This game absolutely set the tone for NU-UT in the Big 12
Second choice: '09 Big 12 Champ. vs Texas. I was at that game, it was absolutely devastating. It would have been a gigantic statement for Husker football.
Third choice: '10 Big 12 Champ. Again, big statement game, and the opportunity to leave the Big 12 by winning the championship.
Fourth choice: '83 Orange Bowl, beat Miami, get Tom his championship, yadayada. But I almost like the iconic loss.
Fifth choice: '01 Colorado. A piece of Husker football died that day, and I think we have yet to get it back.
Others that come to mind:
02? home vs. Texas
That loss at Texas in '99 which was our only loss (Texas theme is pretty evident)
'96 Arizona State
'93 Orange Bowl vs FSU
Some embarassing losses, such as
'09 ISU
the 70-10 TTU game
76-39 vs. KU