Everything is benchmarked or compared to 45acp for stopping power.
Its not the number of beans you can launch but the quality hits that end the confrontation.
IWB holsters conceal the best and are comfortable...Milt Sparks Summer Special is superb !
Choice of firearm: something you can shoot well with.
Considerations: Weight...SIG/Glock/Scandium S&W are lighter to carry but may have slightly more recoil impulse....doesnt matter in an encounter...the fact that you were carrying make the difference.
Fanny Packs: Comfortable but you are not fooling anyone ...may have a deterant factor to crooks, alert factor to Police Officers !
JMHO....9 works, 40S&W most carried by LEO's, 45acp by shootists !