I get the question all the time.
“Okay Josh, so what metrics do you really care about?”
None. Metrics are an automated solution to something that cannot be automated. It tries to detect the link “value” of a domain, without a human actually having to check it.
Domain authority is very similar to citation flow. This can be inflated by hitting your tier 1 links with a big amount of backlinks, in a “buffer” strategy.
Trust flow is based on a graph system which depends on 2 major factors, from what I can see. Those factors are, how close in the “web graph” you are to an authority website. From what I’ve researched and read, Majestic set a high trust flow value manually to some high authority websites, like ~50 domains. The trust flow trickles from those ~50 domains and somehow reached you. If you’re not in that graph, then you won’t get much of a trust flow. It’s a good system but it has it’s flaws. The second factor is simply the outbound links. If a page has 25 outbound links, then the trust flow will be diluted, which is exactly how link juice works over at Google. If it’s just 1 link, then it will push a lot through, which is why I based my domain services around authority links. It’s not proportionally divided in a linear distribution, but there is correlation.
Ahrefs also has a metric, and the distribution for that is often quite high in the lower part of the distribution. A domain with a domain authority of 20 might have a rating of 40+ on Ahrefs.
“So, when should I use metrics?”
When you’re sorting through massive amounts of domains and cannot justify manually checking all the domains. If you have 10 domains to check, you’re much better doing a manual inspection. If you’re sorting through 75,000 domains, then you will need metrics of some sort to help you get through them.
At the end of the day, metrics are an automated solution to an analysis that shouldn’t be automated, but rather checked manually.