They only played against each other at club level - and Manly won every game played between the two clubs between 1992 (the year Harrogan made his Origin debut) until the 1997 Grand Final. During the best part of the two players' careers (1990-1999), the two clubs played 18 times - Manly winning on 12 occasions, including two of three finals (the 1997 Grand Final was their only loss to the Knights in a final in this time).
Of the nine seasons 1990 to 1998, Newcastle made the finals on four occasions (1992, 1995, 1997, 1998), including one grand final and one premiership. Manly made the finals on eight occasions (only missing out in 1992) for three grand finals and one premiership. They also won three minor premierships to Newcastle's none.
Between 1990 and 1998, the Knights finished behind Manly on the table every season apart from 1992 and 1998.
Using personal success as a guide, and remembering that rugby league is a team game, I would have to say that Carroll trumps Harrogan.