Yesterday, at the pistol range, a new range member was shooting his new enhanced Sigma 40 S&W. Very accurate, but about every third round was a failure to feed.
We examined it and can't tell if the feedramp needs to be polished, whether he was having magazine problems, or whether it was the ammo (some of the UMC stuff I've never had good luck with.)
We told him to try a different brand of ammo -- perhaps the range ammo (cci blazer) -- put another 100-200 rounds through it, and if it was still malfunctioning, let the range's armorere (Smith and Glock trained) tweak it. If that doesn't do it, send it back to S&W with a list of the problems.
The Sigma's reputation has been horrid, and I've never personally talked to a shooter who had good luck with one. I have seen many messages, like those on this site, which heap praise on the gun.
I'd suspect that a higher number of Sigmas are a problem than is the case for other S&W, Rugers, Berettas, etc. But I also suspect you'll find some of them shooting quite well, and very reliably. Sort of like the luck of the draw.