it would also depend on the offensive set of the team you play. There are certain set plays which will give the ball more to the PG, SG,SF,PF or C, then they wil be able to dominate you.
from experience, when the set play is left on dynamic, in other lives, especially 2003, PG really dominate as in others have said. but this year, this has toned down quite considerably. it would still be better if you set the plays of your oppnents.
here's some tips.
for star PG, leave it on dynamic or use box plays (if they average a lot of assists, use the motion play, PG would also score a lot in this)
for teams where SG's usually do the shooting, use the stagger play. secondary break also does this but i go more with stagger.
for star PF's, either use the Flex plays or just leave it on dynamic. Double high also gives them some FGA's. Zone motion also gives the PF more opportunities to shoot.
for star C's, definitely sideline triangle. of course if you go doubleing the C's, they'd pass the ball out and the opther polayers are forced to shoot.
for star SG's and SF's, the best is the Box play.
for star Sf's with good 3pt shootin and star Pf's, use the Zone Buster play. I use this when i play against Larry Bird and Mchale's Celtics
hope this helped.