And the best backcourt tandem in 76ers history is...Costello and Greer.
The anchors to one of the greatest teams in NBA history: the 1966-67 Philadelphia 76ers. While Costello may have been injured for a good portion of the year (and was replaced admirably by Wali Jones), he was able to return for the playoffs and help the Sixers capture an NBA title and ending the Boston Celtics' eight-year reign.
Greer was one of the NBA's best long-range shooters before it was popular. He was certainly the beneficiary of Wilt Chamberlain's presence in the middle, but his offensive talent was such that he was able to succeed regardless of who was on the court.
For his part, Costello was one of the NBA's most solid all-around players at the PG position, providing superb defense, on-court leadership and playmaking ability that helped propel the Sixers past the Celtics, and to the top of this list.