Which metric would best reflect success in driving conversion?

The selected answer Purchases is correct because the metric "Purchases" directly reflects the success of an ad campaign in driving conversions. Conversions are typically defined as actions taken by customers that result in a desired outcome, such as making a purchase. While other metrics like detail page view rate or impressions can indicate interest or exposure, they do not directly measure whether a customer has completed the intended action of purchasing the product. Therefore, "Purchases" is the most accurate and relevant metric for evaluating conversion success.