It depends on what you want to achieve and how hard that goal is. In my experience (speaking about giving off link juice), "niche specific" is just an illusion that allows you to feel comfortable sleeping at night despite having your PBNs point at your main site. When I say that, I am assuming that the other PBN in this debate is a general PBN but the page where your link is found has niche-relevant content.
So it would be: niche-related PBN = general PBN with niche-related content (contextual link)
If you are talking about RANKING the PBNs for your keywords then niche-specific is obviously better.