Limited 10 -- major scoring requires .40 caliber or larger and the minimum PF. There is no 9mm major or .38 Super in Limited/Limited 10.
Open -- basically, as long as you meet the minimum PF, you are good.
Production -- if you shoot production, then everything is minor, irrespective of the caliber as long as you meet the minimum minor PF. I have read some people like shooting .40 caliber and load lower PF as the gun shoots "softer." I have no personal experience here.