The Sig will be decent, and I hate to be "that guy", but why not a Colt? I'd even look at PSA right now as they have deals that include an Aimpoint PRO for very little money. I'd stay away from the S&W. Their top of the line models are ok, but why spend Folt or BCM money on anything but a Colt or BCM, if you get what I'm saying.
Of those two, I'd get the Sig. But if you really want the best gun for the money, a Colt or BCM is where it's at. There's really nobody else out there using the parts that they use. The only reason BCM isn't truly mil spec is because they don't have an inspector on site. Otherwise, they're quality is on par with Colt. I know in some instances, BCM has rejected over 50% of their stuff because it didn't meet their strict standards. Most other companies would let it pass and find other slightly out of spec parts to assemble with it.
For range use, almost anything will be ok for now. But if you have any plans to set it up for home defense, plan on taking any classes, or just want a rifle that will last you for decades and will work when you need it, buy quality.
Having said that, I think the Sig will do fine. I wouldn't buy that S&W though.
Keep in mind when I'm talking about Colt and BCM, it's because they can be found at $1,050 or so.... I might not suggest it as strongly if you would be stuck paying $1,400 like some shops sell them for.