However, let Sigma be your choice for one of these two reasons: Either you need a reliable gun and don't have much cash, and you're OK with learning to fire a gun with a heavier double action; OR you are looking for a good choice for a second gun to stick in the nightstand or another part of the house so you have that area "covered".
Those who complain on here, constantly slamming Sigmas miss the point...NO, they don't fire like a $1,000 gun; THEY'RE NOT SUPPOSED TO. Sigmas are like a Honda Civic...no flash, no luxury, but RELIABLE. You want a Lexus, then go buy one. I'd rather have two Sigmas on opposite ends of the house than one Sig or Kimber that I might not be able to get to. In addition, when you're in a self defense situation, the trigger pull can be 20 pounds but because of this little thing called adrenaline, YOU WON'T CARE. The clip will empty just as fast as your $3,000 Wilson tactical. Got it?
Now, on to the M&P. They are pheonominal to say the least. I own two. For a hundred bucks more than a Sigma, you can get one of these. You get twice the quality for that extra hundred, maybe more, especially with the rebate and the two free mags. I cannot recommend these guns more; I own the 9c and the 45, but I have shot the full-sized 9mm as well. At the gun show last weekend, these were running about $350-$375 after rebate, and you have four mags. Incredible deal.
I have not shot the SR9, but I have held one. Not bad in the hand; I'd like to shoot one. It is a big step up for Ruger, their guns normally feel like a brick. The SR9 is competitive for sure; but ergonomics are not quite as good as the M&P. I would imagine the M&P would have scored equally on that torture test, which I have read. I can't put the SR9 down, but the M&P .45 did get handgun of the year (the .45 is based on the same frame as the .40 and only slightly larger that the 9mm). I do give Ruger props for the low profile external safety, which is something M&Ps dont have. My .45 has an external safety, but it sticks out like Dumbo's ears. I think this is the only M&P caliber that has that. Look for this Ruger safety to be copied, along with the chamber indicator, which is more noticable that the M&P's chamber indicator that is hard to see in low light.
Two last factors to consider: Since the SR9 is new, you will pay a bit more right now. You can get an M&P cheaper right now, plus four mags. Also, Smith offers a lifetime warranty on M&P models, compared to a one-year on the Sigma. I had to use this warranty on my 9c after I failed to read the booklet on field stripping it (I assumed it was like a Sig) and I broke a small piece of metal off the slide. Totally my fault. They replaced the slide, and paid for overnight shipping both ways, even though it wasn't Smith's fault. Not sure if you'd get that with the SR9, you'd have to check. Even my Berettas (Px4 and Cx4) came with a one year warranty (three years if I registered), so a lifetime warranty is a big deal, especially for a price this low.
The full sized 9mm M&P is the most comfortable gun I've EVER shot. I've shot a lot of guns, and everybody has a different preference. This is a subjective opinion, of course, but the SR9 would have to be one of the greatest inventions ever to make me choose it over the M&P, especially while Smith has the promotion going on through the 31st.