Notifications are binding on all including assessee, department, courts, etc.
However, Circulars are NOT BINDING on assessee, however, they are binding on department. If some circular is beneficial for an assessee then he can take the advantage of the same and department will have to allow the same. If it not beneficial for the assessee then he may refuse to follow.
ISSUING AUTHORITY:-
Notifications are issued by the Govt. under the power given by legislature
Circulars are issued by the Department to clarify some issues or laws.