The KPI I would prioritize for optimizing future native ad campaign performance is engagement rate. This metric shows how actively users interact with the ad through clicks, shares, comments, or time spent engaging with the content. Unlike impressions alone, engagement rate provides deeper insight into whether the advertisement feels relevant and valuable to the audience. By analyzing engagement patterns, marketers can identify which topics, formats, and messaging styles resonate most effectively. It also helps uncover points where users lose interest, allowing for better content adjustments.