Unless you're really worried about price, get the Sig. Of the bunch, the Sig has the best trigger (and it can be made worlds better by Bruce Gray), it is, IMO, the most ergonomic, and I believe it to be safer than the Glock by way of a much heavier trigger pull. I don't want to get into a discussion of Glock safety-the pistol is plenty safe, and I carried one for about a year, but I personally feel safer with a Sig. Dry firing a Sig is also nicer than a Glock due to the fact that you don't have to manually reset the trigger after every pull, but that is a very miniscule aspect of the weapon as a whole.
I have shot HKs, and they're okay, but not nearly what they are cracked up to be, but again, this is my opinion, many people swear by them. I found their trigger to be long, their reset to be weird and long, and I found myself executing some unintentional double taps, although if I shot it more I believe this would not have been an issue to fix. HK customer service is supposedly a bear to deal with, and I prefer not to deal with HK on principle because of their inability or unwillingness to produce products (readily, at least) for the US civilian market (read HK 416).
I own a 229in .40, and to be honest, I have not shot a pistol that I like more, including the 1911 that I sold to buy the 229. The Sig is accurate, soft shooting, and has excellent ergos IMO. I also like that fact that my .40 Sig can be converted to shoot 9mm on the cheap (although a 9mm Sig can not be converted to shoot .40 or .357 Sig), not to mention that .22 conversion kits are readily available now.
I believe the best buy of the 3 to be the Sig, which is why I own one. The Glock works-there is no question about it, and the HK is a nice gun as well, but of the three, if you want the best gun, go with the Sig. Like I said, any will serve the purpose and get the job done, but the Sig is simply head and shoulders above the Glock, and the HK, while a good gun, is just too much in the wrong places IMO.
As some other folks said, the M&P might be the best combination of everything you are looking for, if you do not want to spend the money on a Sig. It is reliable, accurate, durable, and cheaper than the HK and Sig. Choose this if you're on a budget and can not find a used Sig.