I have one of the early SIG 556s, a "JS" prefix.
The only problem I've had is a small tear in the rubber dust lip and SIG replaced that.
Otherwise, I've had no problems, no failures, and the trigger is excellent.
It's a little more front end heavy than most ARs, but then again, it isn't an AR.
God gave you a soul.
Your parents, a body.
Your country, a rifle.
Keep all of them clean.