What Are the Best Book Marketing Services for Authors?

Has anyone worked with the best book marketing services and seen significant results? How do you determine which services truly deliver value and increase sales? Are certain platforms or strategies better suited for specific genres or types of readers? How much should an author be involved versus relying on the service? I’m trying to find reliable ways to promote my book effectively and would love to hear personal experiences, recommendations, or tips from other authors who have successfully used top book marketing services.