I'm ambivalent of 9mm revolvers due to problems with binding cylinders due to the tapered 9mm case backing out and jamming against the recoil shield. Others have had no problem with their versions. If you have one that works fine, 9mm makes the most sense, but you'll likely make a safer call by going .38sp/.357mag.
"You need a shotgun, man, it's got a good spread.
It's easy to load, doesn't have a lot of working parts...ya ain't gotta be that accurate, the further away you are the more **** you hit."