When considering caliber selection, it is important to remember that with their best loads, all modern 'service caliber' pistol cartridges do the same thing to the 'bad guy' - put a ragged-edged hole a bit over a foot deep and about two-thirds of an inch in diameter in his body. Where you put that hole is MUCH more important than a hundredth of an inch or so hole diameter difference. 'Secondary' characteristics, such as muzzle blast and feed reliability, along with controllability in a pistol of a given size and weight are actually more important that illusions of 'stopping power'.

.40 S&W operates at a higher pressure than .45ACP and might be a bit less desirable for home defense use because of its more intense muzzle blast. If greater capacity is required, the 9x19 is the way to go. Also, a more compact pistol can be built around the 9x19 and its shape is inherently more feed reliable than the .40 (or the .45ACP, for that matter).

For me, the .40 is 'neither fish nor fowl'. After considerable .40 S&W trigger time on several platforms, I go with 9x19 for everyday carry - a pair of S&W 3913s, one to carry and one in reserve. If I could afford a third pistol (instead of something more urgent), a .45ACP for nightstand - S&W 4506 or 4566. The .45 would not be chosen for 'stopping power', but for the reduced indoor muzzle blast (there might not be time in certain situations to throw on the amplified hearing protectors kept with my 'bedside kit').