Individuals can select their own default option, but it will only last for that session. Once they log out, the global default settings will display when they start a new session.
To edit the global settings, you'll go to:
onCampus > Settings > Academics
Change the Assignment Center Default Display dropdown to whatever your school wants the global default to be
For individuals to change their Assignment Center Display default, they will go to their Assignment Center and select Assigned, Active, or Due. After they log out, the cookie that holds their selection will be gone.