Starter(Community) plugins are for users who do not have advanced requirements and would prefer to add functionality through extensions overtime.
Professional plugins are usually for users who work in a single role team structure with relatively more advanced requirements than a starter user.
Enterprise plugins are for multi-team, multi-role organizations with complex requirements. Enterprise plugins come with very advanced functionality that are not offered in any other edition.
To be able to compare the editions in a product group, click on the Compare link in the navigation toolbar.