everyone knows that both are sub standerd go with a .45! LOL seriously, both are effective defence rounds, if it is for defenceive use go with the largest caliber you can shoot accuatly, but that usualy means you loose capacity. I trust my .45, but although she can shoot it, a 9mm is a more confadent choice for my wife. As a "revolver guy" I will asume you shoot at least .357 so the .40 should be easily managed, but it is a personal desistion that only you can make.
If the fear of a hi-cap mag ban causes you to loose sleep, buy a hi-cap 9mm while you still can.