Tried a shield when they came out and see a lot of positives due to it's size. but the width was too thin for my hand.
I usually carry a double stack .45 strong side iwb. For my build, I find the double stack 45s are able, but are slightly larger than I want when I need to go somewhere and have to tuck in my shirt.
When I need to tuck in my shirt, my preference is continue carrying a double stack over a single stack, so I grab the M&P40c.
With the radius of the grip and overall height (4.3") with the flat mag floor plate installed it does a good job of not printing without having to look disheveled from over-blousing my shirt to keep from printing.
If I had to pick just one, either the M&P9c or 40c would make an excellent choice for the everyday carry role and would transition well to the home defense role with just a magazine swap. Since they are the same physical size, it's a matter of caliber preference as far as which of the two models to pick.