As a beginner, I’m confused about which one to prioritize more when selecting guest post sites.
nowadays relevancy is more important than authority, so focus on that!
And if you do need authority, PBNs and niche edits are a better choice than guest posts because a guest post will always start on URLs with zero DA, but a niche edit - if chosen properly - can be placed on a URL that already has good DA, which will give power (link juice, authority, whatever you want to call it, it's basically the same thing) to the page on your website that you're linking to.
So, if you need power choose PBNs or niche edits, if you need trust and relevancy (which is more important in the beginning before you establish yourself as a trustworthy authority) you go for guest posts.
Of course, this is generalizing, ultimately you need to know your niche and competition to know which links to go after because not all niches and keywords are equal, some of them require more power from the beginning (casino / betting sites for example), while others (in "white hat" niches so-to-speak) require more trust initially, which is why you should prioritize guest posts, foundation links (aka, profile links on high authority sites like Issuu, Adobe, Soundcloud, Author.me, etc) or even social signals, these can help with building trust (alongside with traffic, which is also important) too if the signals are of high quality (come from real, established accounts with high engagement).