It depends. We know you’ve heard this answer before, but the number varies based on your site load speed, user experience, revenue per page, and other site-specific factors.
That said, ideally, you should aim to bring at least 5 demand partners to ensure competition and improved eCPM rates. As page content isn’t affected by the number of bidders, you can deliver a better user experience with 5+ demand partners.
We advise you to test, analyze, and then decide. In most cases, 7 to 8 is what we see publishers using in their client-side wrappers.