More than one. Here’s why:

 If you have multiple ads that are similar, DSPs can be set to automatically rotate those ads, and as one starts to perform better, it will be shown more frequently. That means your better performing ad is shown more during the campaign, allowing you to get better results (e.g., more people to visit your site) even within the campaign. 

Also, if you have two ads that are similar but differ on some dimension (for instance, a different call-to-action, or different images), you have a built-in comparison. If one does better than another, you can use that knowledge to inform your next campaign. It’s best if your ads only vary in one way rather than multiple, otherwise you won’t know what caused the difference in performance.

Lastly, sometimes it’s hard to know if your ad compares well with other ads in the industry, especially if there isn’t a good industry standard. If you have more than one ad in a campaign, you at least compare it against its ad-mate.

When you make more than one ad of the same type, the system can optimize your performance, and you can check your performance data to learn what message resonates best with your audience. If you give the platform more than one ad of the same type, we’ll automatically put them in an ad group, so they will be automatically rotated and adjusted. If you don’t want us to do this, just let us know.