Typically.
1) Guest post is better in typical situations. Why? It's on a site that's not as exploited and has fresh content regularly . PBNs are built with the sole purpose of exploiting them for back-links and Google usually smacks them and the sites they link to, which don't have a very high reputation / back-link profile from reputable sites
2) Now, if the guest post is on a trash site... Nope.... and some people sell 'guest posts' as part of their sales page on a PBN but a true guest post comes from websites with REAL VERIFIABLE WRITERS. They force some to put "Site post" instead of "guest Post" on sites where outreach is done b/c the people who sell are 'sellers' for high quality sites that are more focused on their journalism than selling guest/site posts
3) If the PBN somehow has a better readership, retention rate, and long-standing reputation........... It might out do the guest post but I've yet to seen this
On this forum , expect a lot of people to say "PBN" because that's what's being sold by some people who make millions off this forum and have several burner accounts and minions doing replies, etc. And i'm not knocking the hustle. Hell, anyone can still try the PBN and it may work but these are just facts I've found.