papersniper... I am equally a fan of 9, 40, and 45. The only things I might have against any of these calibers would be not-so-great choices of what firearm they are fired from!
I think 40 is an awesome caliber, because I love the greater potency than nine and the greater capacity than forty-five. It is a great blend between the two and a vey enjoyable caliber to shoot, as long as one chooses a comfortable pistol to shoot the caliber with.
I have never enjoyed the feel of shooting .40 from a Glock; to me Glocks don't handle the caliber comfortably. But I love 9 and 45 with Glocks!
On the other hand, the M&P40 and M&P40C, for some reason, make shooting forty very comfortable and enjoyable. The BHP does a nice job with forty also. And the most luxurious and comfortable shooting forty I have experienced is the STI Edge, which makes shooting forty feel like 9mm target loads. Simply awesome! Very high capacity, great reliability, and superb soft-shoot ability with .40S&W in the STI Edge.
As much as I do like my M&P45C, for some reasons, I guess I prefer my G30, G21SF, and 1911s more for when I want to launch forty-five ammo. And, I like the G21SF more for home and RV defense pistol choice. The G30 and G21SF are fantastic pistols, both with equal and higher capacities than the M&P45C.
All that said, I am perfectly content with the M&P45C for carry duty. It is a good pistol, chambered in a great caliber.
I can, and do, carry pistols in all three defense calibers. Somehow, however, over the last year, I have naturally and unintentionally gravitated toward carrying the M&P40 and M&P40C, simply because they are easy to shoot well, reliable, accurate, comfortable to carry, and offer a relatively high capacity... in a potent defense caliber. What is NOT to love about that combination???
To me 40S&W is the Goldilocks caliber: not big, not small, just right! ;-) And easy to find during an ammo shortage.