I'm no big fan of the sig, but seeing how a G32 becomes a G19 after a barrel swap. It would make sense to go ahead and grab a G32/23.
For civvies 9mm is more economical but LE is a different story, but even in that light I still would opt for 9mm. SHTF or not, I have a feeling 9mm will be the last cartridge ever fired.
For me it's either 9mm or 45, easier to find and cheaper. You'll notice how people with assault rifles feel secure with such a sissy handgun load.