I am a 357 magnum fan boy so I dont have a dog in this race but if it was me and I was getting a 9mm it would be the subcompact Glock. They work well and are fairly small. To go much smaller you will have to go single stack.
Shot placement is everything! I would rather take a round of 50BMG to the foot than a 22short to the base of the skull.
all 25 of my guns are 45/70 govt, 357 mag, 22 or 12 ga... I believe in keeping it simple