The one thing we will never do is base authority sites from metrics that are specific to one SEO tool.  If Domain Authority (DA) is something you live by, we do not pay attention to it.  It's a Moz metric and we've come across more domains with a high DA but actually worthless than sites that are legitimate.  Typically, the sites we identify, will come with a high Domain Authority.  We identify sites that have high metrics across all of our SEO tools used.  If it scores high with Moz, but low on others, we won't use it.  It needs to be relatively similar across all tools.  A true authority domain will rank for thousands of their own keywords, get thousands of monthly visits and all tools rank them at the top of their niche.