My first auto, several years ago was a sigma...still have it, but it doesn't get much time anymore as I have gone WAAAAY off the deep end buying guns since. I'll say, it's pretty bare bones and almost "cheap" looking in some folks eyes, but I absolutely love that little dude. Its accurate, has never failed to go "bang", and chews thru ANYTHING I've ever fed it. My M&P by contrast is a finicky little pistol.
And I personally think the Sigma has a "limousine" trigger pull.
(long & heavy