As others have said here both are great pistols. I to have a preference for SW .40 and .45 over 9MM pistols, although I do have a Sig 226 in 9MM and a H&K USP in .45 with the light attachment too.
The Sig I carried on duty in the Sheriff's department for awhile (At the time we were restricted to 9MM.) I found it to be a very reliable pistol, easy to maintain and one of the most accurate pistols that I carried. (A real ray gun!) It is also small enough to carry concealed easier then some other full size pistols; however. its still a full sized pistol. Sig also sells the 226 in S&W .40 caliber with a light rail and a couple of different types of actions. In 9MM, my favorite pistol is the H&K PSP, which is no longer made; however, it is still sold used by some shops. (Its a squeeze cocker.) Its fairly expensive if you can find one.
I love my H&K USP .45 , for many reasons; however, it is very bulky and large for easy concelment. It is also easy to maintain and is very accurate and reliable too. I like the variations of the actions offered on this pistol. Mine has them all. I can carry with saftey off and round in the chamber on double action, (My normal carry.) or I can carry it on single action with a round in chamber with saftey on. One can go from single action back to double action with a flick of the saftey. (Handy after the fight or firing is over.) One can also cock the hammer manually and go from double action to single action and place it on safe. Mine spends a lot of time bedside with light attached for home defense.
My recommendation based on your choice of 9MM, is to get the Sig in 9MM with double action and the light rail. Buy four full sized magazines, you'll get two with the pistol and also buy with the Sig night sights or have them installed.
