The main contrast between AEM (Adobe Experience Manager) and AEM as a Cloud Service lies in how they are deployed and managed. Traditional AEM is usually hosted on-premises or as a managed service on cloud infrastructure, needing manual updates and maintenance. On the other hand, AEM as a Cloud Service is akin to a software-as-a-service (SaaS) model, offering automatic updates, scalability, and high availability from the start. This version promises smoother operations, faster time to market, and decreased overall ownership costs.