It really depends on the quantity of PBN sites and whether they're gonna be long-term or you're just going for the churn and burn method as the above gentleman said so. If you're gonna have like 5-10 PBNs for long-term residual income then go for completely unique articles. Either write them down yourself or outsource.
One more thing, while content is indeed the king, make sure to spend quality time in setting up a PBN and make it as natural as possible to avoid problems if of course you're going for long-term.