When it comes to all time great's only three things matter, MVP, FMVP and rings.
Nash is clearly ahead of Parker. Two MVP's and his playing style would eventually be adopted by Pop and turn into the Spurs tiki-taka game of today. He was also cheated out of a ring in 2007 vs Spurs with Tim Donaghy in game 3 and Robert Horry hip check in game 4.
I can not rank Kidd and Paul ahead of Parker because they simply never won any individual awards or rings. 4 rings and FMVP pushes Parker over both IMO. While Parker doesn't produce huge stats he is on a far more balanced team and he is the heart of the Spurs offense of last 3 successful seasons. He also attract the opponent's best defenders (LeBron) and drains their stamina and free up everyone else.
So Magic > Nash > Parker > anyone else for me in the history of PG's. You can say Parker's success is right place, right time, but you can say that about most other hall of famer's as well. I have to take 4 rings + 1 FMVP over . . . nothing's.
Manu is the hardest to rate. He has 4 rings but because of his off the bench sacrifice, he has zero individual awards. He is the greatest six man to ever play the game and when he was the leader of a team, he led Argentina over two dream team's in 2002 and 2004, including the first ever defeat of a full NBA squad. I can not rate him ahead of Jordan/Kobe/Wade/AI as I don't think his style of play and body can carry a team through 82 games and post season as the primary option. But against anyone else? He compares favorably IMO.