Tie between Gillespie and Ernst for me.
Remember, when the camapign started, Republicans sort of gave up on Iowa. They failed to attract their top tier candidate and so got this obscure state senator. Over the course of the campaign, she deconstructed the fumbling Braley perfectly and came across as a real citizen candidate. Cruised to a blowout victory!
Gillespie’s near-upset was just... stunning. Nobody saw it coming. The best sleeper ground game I have seen in a longtime. He and Dave Brat prove that a solid Republican ground game can defy the polls!
Both of them ran great campaigns.