Have to agree with this article.
http://www.gormogons.com/index.php/2013/06/gun-review-bushmaster-xm-15/I own a Bushmaster ORC with an EoTech holographic sight. Great quality, deadly accurate.
I'm by no means an AR expert, but do know for what you'll use the rifle/carbine for 99% of the time, don't get caught up in the fanboy aspect of it. Buy a good quality product and enjoy it. Build vs. Buy. Personally, if it was my only AR, I'd buy. Guns are like money in the bank. If you ever need quick money, you can always sell one. It will be more difficult to sell one that you built over one that was purchased whole.
I bought mine from a friend that was selling it. He bought it, owned it 5 years and only put 200 rounds through it. With that said, if I would have bought it new, I would have certainly looked at Spikes Tactical.