Re: S&W M&P 40c and Kahr PM 40??????????????
I've got an M&P 40c, and I love it. I've had zero problems with it; clean, dirty, 3 different brands and weights of ammunition in one magazine, one handed, weak handed... I can't screw it up. I carry it in a CompTac CTAC holster and have no issues concealing it in anything I wear, from shorts and a t-shirt to jeans or pants with a button-up shirt. Everyone who's shot it has enjoyed it, and I think the recoil is quite manageable for a compact .40.
My wife has one as well, and she loves it. When we got hers new last year, every now and then the slide would lock back with one round left in the magazine. We sent it to S&W (free) and got it back 2 weeks later with a new slide release (free) and haven't had a single issue in the hundreds of rounds since then.
If I had to do it all over again, I would probably get the M&P 9c. 9mm is easier to find around here, cheaper to practice with, and the 9 has two more rounds per mag. Either way though, I don't think you can go wrong. I really enjoy the adjustable backstraps, so you can get a solid grip no matter what size your hands are. Go buy one now, and I think that S&W is currently offering two free magazines or a $50 rebate through the mail. Do it.