I've wondered that myself. The statistics seem to suggest Laver by a hair, or co-equal number 1.
"Laver won 11 tournaments and Rosewall 10; Laver beat Rosewall 15-4 in head-to-head matches."
"A point system for 19 pro tournaments (excluding at least 10 other tournaments) also resulted in Rosewall being No. 1 to Laver's No. 2 but that system granted each tournament the same points and then was unfair to the big events where Laver was superior to Rosewall : Laver beat Rosewall & Gonzales in U.S. Pro; Laver again beat Rosewall in Wembley Pro; Rosewall beat Laver in French Pro."
Maybe it is this "unfair" point system.?
The fundamental cause of the trouble is that in the modern world the stupid are cocksure, while the intelligent are full of doubt.