I would go with a Colt 6920-R Trooper, if you want to save some money to be used for optics, ect. They're available on line for as low as $760 ish. Comes with a 13" Centurion M-Lok rail.

Up from there, I would look at the Colt 6960 CCU. This comes with a light weight mid-length barrel and a 13" Centurion M-Lok rail.

The DDM4V7 is an excellent choice, one that I currently use as my Patrol Rifle while at work.

I'm one of the few on this site who would not recommend a BCM. I got burned by them and attempts to work with their customer service department, knowing it was intended to be a duty weapon, only made it worse.

The KAC SR15 MOD2 is an excellent gun. And if you don't have issues with the cost, I would buy one in a heart beat. But you could buy a Colt 6960 and a backup 6960 for the cost of an SR15.