I have owned several brands of AR-15's, and Bushmasters are my favorite. Great accuracy and reliability, and great fitting of parts.
The Ruger piston driven guns are fantastic, but I'm NOT a fan of rifles with so many rails. I'd rather bolt on the right sized rails in the positions I want than have them integrated. I wish they offered a 2-stage trigger w/heavy barreled model, but no luck so far.
DPMS is my favorite for the budget friendly models. The slick sided receivers can fail to eject when the receiver is cold unless low temp oil is used (winter time before 1st shot). The one's I've had were older single stage triggers, which felt like crap, but as I understand it, their new triggers are better and their 2-stage triggers have always been decent.
In my opinion is that the Colts and Remington's are way too expensive for what you're getting.