Hi guys, it is not about caliber. Of course the size of the hole matters. What matters more is the first rule in any gunfight: have a gun! I have a Ruger Super Redhawk in 44Mag. Will surely make a mess of any attacker, but it resides in my safe, it is too big to carry. My Glock 19 sits on the hip, sleeps under my pillow. Which means I have a gun!
I have experience of what a 9mm can do in the hands of a skilled person. Use what you are comfortable with, the rest is bull****.
Any gun, more than an armslength away when the sh... hits he fan, is of no use, no matter the size the of the bullet.