The only way I'd pick the Sig is if you plan to carry it hammer down DA for the first shot. Sig has the best DA I know of in an auto, hands down. The DA shot of the HK45 is mediocre. The best versions of that gun are the LEM or the V1 (to run cocked-and-locked). I can't comment on the M&P. It has a good reputation but I've never tried one.