To optimize the relationship between two objects in Salesforce, such as Container and Container Bids, where there is a need for a tight relationship and cascading delete functionality, a Master-Detail relationship is most suitable. This type of relationship has the following characteristics:

Cascading Delete: When a record in the master (or parent) object is deleted, all related detail (or child) records are automatically deleted. This ensures data integrity and aligns with the requirement that Container Bids should be deleted when their associated Container is deleted.

Tight Coupling: A Master-Detail relationship creates a strong linkage between the two objects, where the detail (child) record's existence is dependent on the master (parent) record. This is appropriate for scenarios where the child record should not exist without its parent.

Options B (Hierarchical Lookup) and C (Many-to-one Lookup) do not provide the same level of dependency and cascading delete functionality inherent in a Master-Detail relationship.