Oscar Robertson was clearly the best PG in history, only player in history to average a triple double for a season.
Actually the top point guards have some very impressive stats, I can see an argument for Magic or West as well. I got a bit carried away, here are the NBA's greatest PGs, excluding anyone who is still playing in their prime.
Best season:
Robertson - 30.8 ppg, 11.4 ast, 12.5 re
Johnson - 23.9 ppg, 12.2 ast, 6.3 re
West - 31.2 ppg, 7.5 ast, 4.6 re
Iverson - 30.7 ppg, 7.9 ast, 4.0 re
Thomas - 21.2 ppg, 13.9 ast, 4.5 re
Maravich - 31.1 ppg, 5.4 ast, 5.1 re
Cousy - 19.4 ppg, 9.5 ast, 4.7 re
Stockton - 17.2 ppg, 14.5 ast, 2.7 steals
Nash - 18.6 ppg, 11.6 ast, 3.5 re
Frazier - 20.9 ppg, 8.2 ast, 6.0 re
Kidd - 16.9 ppg, 10.8 ast, 6.8 re
Payton - 24.2 ppg, 8.9 ast, 6.5 re
Monroe - 25.8 ppg, 4.9 ast, 3.5 re
Career average:
Robertson - 25.7ppg, 9.5 ast, 7.5 re .485 fg%
Johnson - 19.5 ppg, 11.2 ast, 7.2 re, .520 fg%
West - 27.0 ppg, 6.7 ast, 5.8 re, .474 fg%
Iverson - 26.7 ppg, 6.2 ast, 3.7 re, 2.2 steals, .425 fg%
Thomas - 19.2 ppg, 9.3 ast, 3.6 re, .452 fg%
Maravich - 24.2 ppg, 5.4 ast, 4.2 re, .441 fg%
Cousy - 18.4 ppg, 7.5 ast, 5.2 re, .375 fg%
Stockton - 13.1 ppg, 10.5 ast, 2.2 steals, .515 fg%
Nash - 14.5 ppg, 8.6 ast, 3.0 re, .491 fg%
Frazier - 18.9 ppg, 6.1 ast, 5.9 re, .490 fg%
Kidd - 13.0 ppg, 9.0 ast, 6.4 re, .401 fg%
Payton - 16.3 ppg, 6.7 ast, 3.9 re, .466 fg%
Monroe - 18.8 ppg, 3.9 ast, 3.0 re, .464 fg%