What Is a Good Backlink?
Nothing to do with PageRank as we know it. It has to do with the real PageRank, which has just one secret. Pages that show up in Google's first results have the biggest PageRank, and those are the best backlink sources. Simple, isn't it? But hard to get a backlink from such pages, still the principle stands. The best source of backlinks for your target search query is one of the ten pages that rank well. All the rest about Domain/Page Authority, outgoing links, dofollow/nofollow tags, don't matter so much, but I will get into those. A good backlink is every backlink you gain naturally; I got a good backlink from Wikipedia because my article is relevant to the topic.
So there are plenty of tools showing you metrics and promise to help you rank your pages. Opensiteexplorer, Ahrefs, SEMRush, Majestic, Link Research, Monitorbacklinks, Ubersuggest, all are paid (important because they keep you on a subscription) tools that promise to automate your work (note that all-in-one solutions never work without an expert eye). Domain/Page Authority/Rating doesn't matter so much; it's just a metric. I prefer a tool showing me how relevant a page is to my topic, not even a keyword. The spam score doesn't matter if the page ranks well. If it's good for Google, then the spam score is not a reliable metric. Outgoing/Incoming links again the same as above, Trust Flow same as above; if Google likes the page, I do too. Page traffic would be a good metric if the tools had a reliable way to measure it, which they don't have. Bottom line: start with pages that rank well or the websites that show up in search. If you manage that there's no tool to do it better for you.