Which tool enables the development, QA, and publishing of rich media and dynamic creatives?

DoubleClick Studio (now Google Marketing Platform's Creative Studio) is the correct tool because it is specifically designed for the end-to-end management of rich media and dynamic creatives, encompassing development, quality assurance, and publishing to ad servers. Google Web Designer is a tool for creating HTML5 ads but doesn't handle QA or publishing to the same extent. Google Tag Manager is for managing website tags and tracking, not creative development or publishing. DoubleClick Campaign Manager (now Display & Video 360) is an ad server and campaign management platform; while it serves the creatives, it's not the primary tool for their development or QA.