I used to sell quite a few Rock Rivers, but we've gotten away from them for a couple of reasons. I'll still order one in for someone who wants really wants one.
The biggest problem we had wasn't quality. It was wait times. I know they're popular, but the 6-10 weeks wait every time I wanted to restock even the basic guns was a killer.
I've noticed a few problems in more recent guns. The gas keys haven't been staked as well as they used to be. Not that this caused any issues, but it is one of those little things that can make a difference.
The biggest issue I've seen arose from a PD gun that was brought into us. He wanted to add a single point sling attachment. When PvtPyle went to remove the stock, he found that the retaining ring (whatever it is officially called, I don't know, the thing that holds the tube on) was not staked, but rather it had been loctited on with some siliver stuff. He remarked that that was odd. Don't know why they would do that.
Found out real quick when he started to tap on it, and the ring broke into 4 pieces. Not a cool thing to happen when the customer is standing there watching you work on his gun.
Apparently that ring was just some sort of really chintzy metal. That would explain the lack of it being punched.
We replaced it for a new piece, but that was kind of disconcerting. I don't know when they started using parts like that.
I've heard other things, but haven't personally seen them, so can't say if they're true.
Not big Colt fans here either. I think they make a good rifle, for the most part, but occasionally they do screw up, and from what I've seen first hand, they have a hard time making it right. We had one batch of National Guard rifles here that had over torqued barrels, totally out of spec. And when Colt was contacted, they tried to shift blame, and then tried to say that sure, the barrels may fall off when you shoot them, but that is your problem now, because they sat in a .gov warehouse too long before you tested them.
That said, we've had really good luck with Stag. Haven't had any issues, breakage, or haven't had to return one yet for any reason. We even use their parts for a lot of our custom build stuff. If you want more different configurations, or some tricked out stuff, I recommend CMMG.