who had more success as singles, Travis Parrott or Pierre-Hugues Herbert
Travis Parrott: Travis Parrott (born August 16, 1980 in Portland, Oregon) is an American professional ATP tennis doubles player. Travis Parrott:  He is primarily a doubles specialist. Pierre-Hugues Herbert:  In singles he has reached one ATP career final (at the 2015 Winston-Salem Open), and achieved his career high singles ranking of World No. 64 on 14 August 2017.
i don't know