If its to be the end of the season, day after Thanksgiving game, then I opt for Iowa - by far. They are geographically very close - allowing easy travel and they have a lot of fans around here/a shared border - so rivalry would be natural. Most Iowa fans I have spoken to seem to embrace the idea.
Penn State - not soo much. Firstly, travel during Thanksgiving weekend stinks. No way I want to set foot on a plane that weekend. I would much prefer to drive to an away game. Especially when considering distances - and Penn State is a long ways away. Second, despite our past with Penn State (a few games played and a gripe over post season honors), I really don't get too excited about the idea of playing them. More than a Northwestern or Indiana at least, but not the tops of my list. And did I mention how faaaaaar away they are?