An advertiser has launched a Value-Based Optimization (VBO) campaign to promote their mobile app. The campaign is focused on maximizing the revenue generated by high-value users. At the end of the campaign, the advertiser needs to assess its effectiveness and determine if it met their business objectives. Which metric is BEST to evaluate the performance of their Value-Based Optimization campaign?

Return on Ad Spend (ROAS) is the best metric because VBO campaigns are designed to maximize revenue, and ROAS directly measures the revenue generated for every dollar spent on advertising. This directly aligns with the campaign's objective of maximizing revenue from high-value users. Click-Through Rate (CTR) measures engagement but doesn't reflect revenue or value. Total Sales shows overall revenue but doesn't account for the advertising cost, so it doesn't indicate efficiency. Cost per Acquisition (CPA) measures the cost to acquire a customer, which is important, but it doesn't inherently reflect the value or revenue generated by those acquired customers, which is the core focus of a value-based optimization strategy.