Although these four products are branded as CMS, I do not think they are truly comparable. Drupal and, as far as I know, Joomla is a CMS web publication (or WCMS ), they are designed to create websites and manage their content. They are not designed as general CMS, DMS or ECM . Alfresco, and possibly Magnolia, are ECM / DMS for enterprise content management.
For example, being managed in Drupal (given sufficient effort and custom PHP code), a complex multi-agent workflow for multilingual documents (PDF, Office, etc.) is probably easier to manage with Alfresco. And Alfresco is probably not suitable for managing web content with an easy publishing workflow and user-generated content.
Having managed content published on a website does not mean that it should be controlled by the same tools that the website managed. For example, using the Drupal CMIS module, you can link it to Alfresco (or any CMIS ECM compatible) to manage your corporate content in suitable tools, but publish parts of it on the Drupal website.
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