Sherrod Brown over Josh Mandel
Sherrod Brown has good aspects overall that out number his negative aspects. Especially Chiron Trine Jupiter (twice) and Chiron trine Ceres in the progressions. In his transits he has Pluto conjunct Chiron, Ceres contra-parallel Uranus. While he has some negative aspects they are not nearly as bad as the the ones Josh Mandel is dealing with. He has Saturn opposition Chiron (twice) and Saturn in-conjunct the Earth/Moon complex. He has quite a few good aspects but I think it will be hard to overcome the negative influence of the 2 above.
Everyone who has been selected to run for office will have good aspects or they would not have been chosen, the difference maker is the number of negative aspects compared to your opponent. Based on the above I'm giving the nod to Brown.