Rock River Arms.
But between a Bushy and a Colt, I'd definately take the Bushy. Believe it or not: Bushmaster is the most milspec rifle out there. Bushy has the chrome lined bbl, standard milspec fire control components, and the lower will accept a auto sear (if you should buy one later down the road). The Bushy is also as you stated, cheaper. Customer service is top notch!
I personally don't like the Colts. They are way over priced for starters. They use odd sized lower reciever components---not mil spec. Yes the Colt will accept an auto sear (I think). Yes the bbls are chrome lined but big bucks. Their quality control can be a bit loopy as well as their customer service.
I'm not sure if even the Colt is LEO marked. If it has a true M4 bbl then it's only 14.5" in length. Even by permanently affixing the A2 flash suppressor you still would'nt be to the 16" minimum. Extra paperwork and another $200 there. (Or a Vortex/Phantom f/s)
All in all...For me, Colt is the one that is "close but no cigar". Get the Bushy. You'll have a better rifle with extra $$$ to spend on a tac light, scope, mags, ect.