I think we have to separate quality/safety and pure strength/linkjuice here. A good guest post is certainly not stronger than a good PBN link, it won't outweight 60 PBN links.
I'm not a friend of mixing blackhat with "whitehat" (well, buying links is never whitehat). Either you willing to take more risks and pay less, then I'd go the blackhat route all the way. No need for expensive guest posts if you are mainly ranking on PBNs anyway, that's just wasted money without lowering the chance of getting busted by Google. Or you want the longer, more expensive but a lot safer route via guest posts and so on, but then I wouldn't mix in risky PBNs, but stay on the safer side all the way. Both are good options, but I'd consequently pick one.