Main Idea: It is better to have ammo and not need it than need ammo and not have it.
Examples of pistols that meet the criteria of 10+:
45 acp: Glock 30SF / 10 + 1
40 S&W: Glock 23C / 13 + 1
9mm: Glock 19 / 15 + 1
Those Glocks are concealable with light clothing and offer at least 10 + 1 round capacity (+ spare magazine)
As can be seen in this video, some people are hard to stop and additional rounds may be required.
http://www.liveleak.com/view?i=e75_1464135562
It sounds / looks like ~7 shots were needed to stop one guy with a knife.
Examples of pistols that meet the criteria of 10+:
45 acp: Glock 30SF / 10 + 1
40 S&W: Glock 23C / 13 + 1
9mm: Glock 19 / 15 + 1
Those Glocks are concealable with light clothing and offer at least 10 + 1 round capacity (+ spare magazine)
As can be seen in this video, some people are hard to stop and additional rounds may be required.
http://www.liveleak.com/view?i=e75_1464135562
It sounds / looks like ~7 shots were needed to stop one guy with a knife.