...lol.... that one got my morning coffee coming out my nose....
I'd vote 9mm for just punching paper because if you dont' reload it's usually cheaper than .40 S&W to buy and if you do reload might even have a slight advantage on cost there, too.
However, given the difference, in ctgs if it was a SHTF scenario and I could only pick one handgun I'd go with what I know best: Glock 22 .40 S&W stoked with Speer 180 gr Gold Dots.
So, in this poll I vote .40 S&W.
Bottom line, if it's punching paper or otherwise, it's still shot placement that trumps cartridge every time, though.
My .02
NAA.