Between the 9mm and 38spl I would also lean towards the 9 with BB flat nosed bullets.
I was carrying a 22lr revolver when I tangled with three feral dogs. It was the only handgun I had at the time and I had it stuffed with CCI Stingers. It worked well in the moment. After that though, I got to thinking what if I were to run into something bigger. I moved up to a 45acp then later a 44mag.
My advice ... carry what you have but make it as mean as you can with the proper ammo. Plan for the future if you think something bigger may be needed.

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John