First off, I am pretty certain that Smith and Wesson does not make an M&P 40/45. They do make pistols in both of these calibers but not in the same gun for conversion... as far as I know.
That being said, I have both: an M&P 40 4.25" barrel and an M&P 45 full size with the 4" barrel. Both are excellent semi-autos and their ergonomics and general feel in the hand is among the best out there. The M&P 45 4" is one sweet gun. Only down side is its 10-round magazine.
Either one of these fine pistols would serve you very well and since you're familiar with the .40S&W, you might want to lean in that direction. The M&P 40 is a little more slim than is their .45 conterpart which may make it more convenient for carry. Very accurate guns. For carry and SD at home, I would opt for the M&P 40 over the 1911. And yes, I do own 1911's.