We have both the S&W M&P 15-22 and the Sig 522 (green). Each boy picked one. ChattanoogaPhil pretty well summed up most of my feelings.

Additional single data point of our experience: Our 15-22 had the Out Of Chamber detonation experience and was totally replaced. The 2nd one has been perfect for over 2000 rounds. The 522 was perfect out of the box, has about 3000 rounds now and feeds and fires everything and anything.

I have used S&W customer support 3 times (we have several of their products, and only the 15-22 OOC was the guns fault), and had 3 excellent experiences. I have to say that their support was so good, I really leaned towards S&W when looking for a .223/5.56 AR15. I have not needed Sig support.

The Sig hits one pet issue of mine, no bolt hold back on last round. So it's out for me.

Each boys likes his the best. I like the 15-22 so much, that when CDNN had the S&W M&P15 OR ("optics read" .223 AR15) for $599, I bought one. Which by the way does not come with sights, which I approve of because I can get it cheaper and buy whatever I want, not arguing, just saying that's me.

But really I think most would enjoy either, they are both fun, cheap shooting.