It's less expensive for a reason. I'm not sure what that reason is, because I've never seen an example of Eagle Arms.
Armalite is very diplomatic about skirting the issue. They want to sell both. I assume (here we go) Eagle Arms to be of lesser quality, because they are cheaper. I wouldn't buy one, because I am a contractor and I see the difference between brand A and brand B all the time. I want to spend my money on the best and be happy. Not save two hundred bucks and regret it.
Not very informative regarding your question, but I suggest brand A.
Actually, if you are shopping for an AR-15, I recommend a Bushmaster.