A bit long, but here's my take on the 3...
I've shot the H&K USP in .40, Sig P228, and the S&W MP in 9mm.
I grew up on the USP and absolutely loved the pistol as a teenager. H&K is known for their reliability, and the USP functioned beautifully. I also loved the feel of it.
After I joined the Army, I began using training with the P228 more than I could have wished. At first, the P228 was "nice," but as I used it more and we did more training (threw more rounds down range in this last year than most of you would believe), I have really come to love this platform. I have never had a problem with it through all of the torture we have put them through.
Oddly enough, I just fired a box through a S&W MP 9mm this evening. I was not overly impressed with it, but I didn't have a problem with it either. Its kind of hard to pass judgment on a pistol after only 50 rounds, however. I will fall back on being taught that Smith is for revolvers, not auto's. There are too many other companies out there making quality auto's.
In all, I have gone back to shoot the H&K after training so extensively with the Sig, and it's just "off". I was so convinced that there was something wrong with the sights that it got sent to an armorer. After two armorers shot the pistol and confirmed that everything is fine on it, I am convinced that the problem is one of ergonomics. The P228 is so well balanced, and fills the hand so well, that it feels natural to shoot, where-as I have to adjust for the HK. I have to admit that the Smith & Wesson felt good in the hands as well, and my shot groups were fairly tight with it at 25m. While you may not be too worried about "hell and back" reliability (are you planning on dragging the pistol through swamps, deserts, or arctic glaciers?) the fact remains that both H&K and Sig make quality reliable firearms. As I said before, I never had a problem with the 228- even through all the rounds of straight up torture and abuse we put it through. If price is a factor, Smith & Wesson has it hands down. But I am a firm believer that you really get what you pay for with that.
All in all, I vote Sig hands down. The 228 is a little pricey, and hard to find, but well worth it ("I just found a nice one at the place I shoot for $500. I bought it for my son for his 21st birthday" -1BlindRef The bastard who got that 228 from his ole man is a lucky one indeed
- what kind of father actually gets his son a 228 for his 21st birthday? Lucky punk...
). It is a quality firearm that will last you a long time. It is well balanced, and the double stack mag fills med and large hands beautifully. Add Hogue finger-groove combat grips (which you can't do with the USP), and your talking about a firearm that truly feels like an natural extension of you. The 228 is big, but if you have a large frame (or a large jacket and the discipline to actually practice your draw), it works for concealed carry. Maintenance is incredibly easy for the 228, and Sig even has a program to inspect your used Sig. They will replace all the springs, look for maintenance issues, and slap new night sights on for about $100. You really can't beat it (I just sent mine
). The last point is the investment value. The 228 will at least hold its value if not go up. They are no longer in production for the civies, and there is a demand out there. It is a quality firearm, and if you do what little you need to do in order to take care of it, you'll be set.
The other two might fit some of these points as well, but the 228 is the whole package. I hope this helps. Let us know what you end up deciding and why! Good luck; Happy shooting.