Final answer:
To capture subscriber preferences in Salesforce with multiple possible subscriptions, a Multi-Select Picklist field is the best choice since it allows multiple selections to be made from a list of options.
Step-by-step explanation:
The best custom field type to capture subscriber preferences in Salesforce, when subscribers can be subscribed to a range of offerings like magazines, newspapers, books, and e-books, would be a Multi-Select Picklist field. This field type allows users to select multiple options from a list, which is appropriate since a subscriber can have multiple subscriptions at the same time. A text field would not restrict input to predefined choices, a picklist field allows for only one selection, and a formula field is used for calculating values rather than choosing them.