I'd have to say Nebraska. A win against either would be monumental for Southern Miss, and totally devastating for the opponent. Historically, MSU is a program that is capable of losing against anybody in any given year. They don't have a history of being a juggernaut from one year to the next. If Maine is capable of pulling off a shocking upset against MSU of the SEC, why can't Southern Miss? While predictions don't mean much, I've noticed several pundits are predicting them to finish 7th in the SEC West division.
But the main reasons I think Nebraska is tougher is: 1. The game is on the road. 2. It's Nebraska's homecoming game- so more motivation for them to put in a good performance. 3. We play them several games into the season. If NU has any early season problems that would be advantageous for us, they will probably be fixed by the time our game comes around.
Abdullah is gone. But Nebraska usually reloads, and should have some decent running backs taking his place.