I'm with USAF385 and madmedic1955 on this one.

Use what YOU shoot well not what is sexy to everyone else or what a "real man" would shoot. If you shoot a 9mm better than a .45 then there is a huge advantage in that.

Understand that no handgun caliber is going to be the end-all, be-all when it comes to gun fighting, but some solid hits with a 9mm are infinitely more helpful to your cause than a bunch of misses with a .45acp.