For the guest post, your content has to be unique.
You should publish unique content unless you're certain that the publisher doesn't care and only wants your money.
One key benefit for unique content has little to do with SEO.
While we know that there is such a thing as a duplicate content penalty, it works indirectly.
I'm not going into that, but I just want to throw that out there.
The key benefit I'm talking about when creating unique content for a guest post is that you are pushed to create readable content and deliver solid value.
Why should you bother with this?
Well, if it's a guest post, there is a chance that your brand will get in front of the eyeballs of people visiting that site.
Even if it's a PBN, there is still a chance that the page will rank.
Never miss an opportunity to make your brand shine.
And the good news is putting your best foot forward in terms of content quality isn't all that hard.
You will be fine as long as you follow a well-defined checklist of quality control steps.
I suggest that your content at least passes OneText or Quetext screening.