It's definitely not Ohio State vs Indiana.
I'd keep an eye on North Dakota vs Utah. That would could end up being a good game. ND ended up only 7-4 last year in FCS but they played in one of the two toughest conferences there and return a ton of players. They're a solid dark horse pick to win the FCS this year and we all know how top tier FCS teams do against mid tier P5s. (If not, North Dakota State beat Iowa last year, Portland State beat Washington State (2015), Citadel beat South Carolina (2015), Eastern Washington beat Oregon State (2015), James Madison beat Virginia Tech, Richmond beat Virginia (2016), and plenty more. And of course Appalachian State beat Michigan, Georgia Southern beat Florida and my William and Mary Tribe beat lowly Virginia.