I'm not sure you can even compare the two.
Parker fits SA's style, and Billup's fits Detroits.
San Antonio needs a point who can drive to the basket. Billups is best backing and posting up his opponents. That would interfere with Timmy's game. Timmy is our post up guy, not Tony.
On Detroits team, Billups is probably their best Post up player. Rashid really ain't a post up guy.
2 totally different styles, for 2 different teams. The only similarity is tenacious defense. Billups can't guard Tony's speed, and Tony can't guard Billups size. Billup's is detroits #1 option...Tony's really #2 or 3...disregarding his quick start this year.
So I definetly wouldn't take Billups on our team, we don't need a post up guard, tho the assists would be nice. And I don't think Detroit would take Parker on their team on a head to head switch. They've gotten used to have a post-up guard, and need those assists from Billups. San Antonio gets our assists from Tim and Manu.
2 of the best point guards in the league...providing 2 totally different styles of play.
Viva la difference.
And having said all this...I still thing the best pure point guard in the league, is that little Canadian soccer player dood. Him, I'd take over Tony or Chauncy.