Both guest posts and niche edits can help with SEO when done properly. Guest posts provide fresh, relevant content and brand exposure, while niche edits add links to existing articles.
I agree with both points above, and I would decide by the page rather than the tactic alone. A guest post makes sense when you need a fresh, relevant piece where the link fits naturally and you can control the context, the anchor and the surrounding explanation. That control is also why it feels safer, as WolfyG said. A niche edit can be the better fit when the existing article is already relevant, still getting attention, and the link genuinely adds something to a point the article already makes, rather than being squeezed in. Where I would be careful is with a niche edit on a page that has drifted off topic, has not been updated in a long time, or where the new link changes the meaning of the paragraph. In that case the faster, lower-cost option can end up looking forced. So I usually ask whether the target page would still be worth linking to even without the SEO benefit. What kind of page are you weighing this for: a new page that needs context, or an established article where the link would fill a clear gap?
I prefer niche edits when the existing article is already relevant and has solid traffic/authority. They’re usually more natural because the link is added to established content, and you can target a page that already has topical relevance and backlinks. Guest posts are better when you want more control over the content, anchor text, and the context surrounding the link.
I'd lean toward guest posts, especially when there's something genuinely useful to share, like original research, a case study or practical advice. A good guest post can introduce your brand to people who are already interested in the topic. That's valuable even beyond the backlink itself. I will also pay attention to whether the article actually brings relevant visitors over time, rather than judging its success only by SEO metrics.