M&P is larger. Are you willing to carry the larger pistol? I'd recommend the M&P because it won't need as much break-in time or any at all. I've fired both and I can't say the Kahr is comfortable. Although it's intended purpose is not the range. I know a guy who had a Kahr pm40 which he could not get running properly, jammed a lot. Even after a trip back to the factory. I'm sure there's other reports on the net about them and having no issues at all. Such is the nature of firearms. The M&P holds more rounds if I'm not mistaken as well. Consider that too.