Based on how Google has been behaving lately and the public noises they've been making, my guess is that guest blog posts using real content and built on high-quality, relevant domain names would be better investments.
You have to understand that building PBNs can get quite expensive, and you still have to use quality content.
And given how Google has been waging war on link spam and blackhat techniques and whathaveyou, one can easily be forgiven for thinking that the PBN game is in for some major changes.
It may not happen immediately.
It might not even happen a few years down the road.
But if you are paying attention to how Google evolves over time, it becomes abundantly clear that the PBN game and the way it's being played right now is in for a major change.
Now, does this mean that PBNs are going to go the way of the dinosaurs?
Possibly, but more likely, Google is going to make the terms of the game so expensive or so time-consuming that it probably might not be worth it for the typical SEO a few years from now.
I suggest you build real websites with real content and communities.
Thanks to all the SEO keyword tools and content optimization resources available out there, you should have all the resources or ingredients you need to come up with something that delivers solid value to the lives of your real, human, organic community.
Remember, if you build your house on a firm foundation of rock, chances are, you would survive even the worst thunderstorms.
On the other hand, if you were to build your empire on the shifting sands of search trends or PBN strategies, you may not have much of an empire left after a few years if you pick the wrong path.
There are many different ways to build a PBN, of course, each with their own distinct cost profile.