I own several Sigs, including a P-228, and a P-226 in 9mm. I also own a 6906, and a 5906.
I carry the 6906 daily, and my 5906 goes to the range regularly. Sigs are nice semiautos, but they lack the really nice DA trigger pull the 3rd generations have, as well as S&W's wonderful 3 dot sights. I don't know what Sig was thinking, with their 'post' on the rear sight, and the 'dot' on the front sight.
Perhaps they were thinking of 'dotting the 'I'? I don't know. You'd think Those guys in W. Germany would realize that three dot sights are the way to go, and just put them on their Sigs. It's a proven system, and there's not patent on it.
But, my Sigs just pretty much live in the safe, and my S&W's get out and get shot regularly. I LIKE the weight of my 5906; it really soaks up the recoil, and makes follow up shots so much quicker. Did I mention that the 3 dot sights are really nice? They help with follow up shots, too.
I've always wondered why Sig made the P-228 (And P-229) almost as big as the P-226. The P-228 is a 'full sized' semiauto, in my mind, while the 6906 is just enough smaller to really make a difference. The 6906 only gives up one round in the magazine, (12 for the 6906, 13 for the P-228), yet the grip of the P-228 is substantially larger than the 6906. Enough larger that I can conceal the 6906 much more easily than the P-228.
Sig makes nice semiauto pistols, but, just a few differences make the S&W's much more user friendly pistols, IMHO.