I have the colt LE Advanced 6940 and well it is by far the best I have owned or shot. I love that rifle. I did need to do just a little trigger work to smooth it up a bit but that was it. It is a tack driver on the range and has held up to everything tactical that I can through at it. I will be giving it a lot of use as my primary duty rifle. I paid 1300 for it NITB which I think was a super deal. It is chambered 5.56/.223 and has a 1:7 twist. It eats any ammo that I feed it but I like the M855 the best and it seems to enjoy it aswell.
Now when I made this purchase I was looking for a new duty rifle for my work(PMC/PSC) so I had to have one just little better then a plinker so to speak. But there are many good rifles out there, just know what you are going to be using it for and go from there.