The colt is a great choice or you could get a nice Daniel Defense m4, they have quite a few options and configurations to choose from. Their barrels are CHF 1:7 twist and all but one of their rails they offer are free float, whether they are 1 piece or 2 piece. It will be in your $1,500 price range as well. I have a DDM4v5 and love it.
Here is mine
Nice gun. That's good to know, I didn't know DD barrels were CHF. I wonder if the colt barrels are?
Whole lotta of $$$$ for just a name stamped on the side...................build your own and get just as much reliability, save $, and put that into ammo & training
If you want to reach out and touch something, you might consider one of the National Match versions from Armalite or RRA; or just a rifle length versus carbine length version from any of the makers you are partial too. Just putting it out as a suggestion because you didn't really say what you want it for.
I mainly want it for recreational use, and home/self defense. I'm not into competition shooting or anything like that. Also, do all Daniel Defense's have a gas piston system? Do any of them have DI?
If you ever plan to take a class, go with the Colt. BCM is also a good option, but with what Colts are selling for these days they are pretty close on cost.
No you can't build an AR as reliable as a Colt for less money. You can build less for less though, pretty easy.
As far as the Sig goes, if it priced really right it would be ok for recreational use. They are nothing special though, and if it is within a couple hundred dollars of the Colt/BCM option above it would be a stretch to say it is worth it.
No tinkering required :
http://www.laruetactical.com/16”-larue-tactical-predatar-556
You said $1,500 is your limit.