any gun is better than no gun. any size is better than no size. The key is what can you carry? And what are you going to carry everyday. Should it be size? Weight? Size .25, .32, .380, 9mm and so on. I would go for a largest cal. I could carry, and then have a back up gun.
The mag capacity should not be a factor for PP, it should be familiarization and practice with your choice, comfort and carry. Reaction, muscle memory and well placed shots should get the job done quickly and with hopefully, no more than three shots fired.
Now if you plan on taking on many adversary's, I suggest an additional mag or two.