Evaluating spend and performance trends and determining ROI is a structured analytics task. In Microsoft 365 Copilot, the Analyst agent is designed for quantitative analysis workflows: it can interpret tables, analyze datasets, identify trends over time, calculate metrics (such as ROI), and present results clearly (often including charts or summarized insights). This makes it the best fit when your goal is to compare marketing channels and understand which ones are delivering the strongest return based on last year's data.

Chat (Option B) can help you brainstorm questions or explain results, but it is not purpose-built for deep numeric analysis. The Researcher agent (Option C) is optimized for gathering and synthesizing information from sources and producing research-style outputs, not performing ROI calculations on internal performance data. A notebook (Option D) is useful for organizing files and keeping shared reference material across related conversations, but it does not itself perform the analysis---you would still need an analysis-capable agent.