Just going by what's been shown on the field to date, I would say that Michigan State has been our best rivalry in the B1G. It's been an entertaining series - crazy comebacks, big upsets, and heartbreaks. Too bad they're not in the same division as we are.
Sam's point about Nebraska not accepting rivalries that are "beneath" them is a bit misguided. It's that Nebraska fans don't accept rivalries, with one exception, at all.
I don't think it's the case that Nebraska fans won't accept anyone not named Oklahoma as a rival. Remember how when we first joined the Big Ten, we had Penn State as a protected cross-division opponent? Quick survey: how many of you would rather have Penn State as the annual regular season-ending matchup, and how many would rather stick with Iowa? And does anyone think that the game would
ever be stuck on Fox Sports 1 if it were against Penn State?