Difference Between the ‘User’ and ‘Group Admin’ and 'Account Admin'

Account Admins 

Have complete control over the account including all user permissions, configurations and billing. They can request account changes and will see a more in the app, including Manage Users and Reports.  

Group Admins

Can see all tasks in a group and have advanced management controls like Archive and Delete. Can create and manage groups including inviting users and configuring tags.

Users

By default, a user can see all tasks in a group they are added into. There are optional restrictions under the Advanced Permissions link to limit visibility to tasks that they create themselves, and the tasks that are shared with them.