I have both and here's my assessment: after I shoot a stage I'd rather be taping targets, resetting steel and talking to friends rather than hunting down my brass for the next three runs.
9mm brass is everywhere, so YOUR brass is not important to your recovery rate only that you pick up as much as you shot, when you pick up what little 38 brass is lying around, if it was shot from someone else's gun, you'll probably give it back to them.
I bought all my 38 brass and I recover it at a rate of ~75%, 9mm on the other hand I have never bought and my stock just keeps growing