What are some factors that affect the delivery of push notifications?

The best choice encompasses a comprehensive understanding of the factors affecting the delivery of push notifications. User preferences and device settings play a crucial role, as users can choose to enable or disable notifications for specific apps, or even block notifications entirely at the system level. This means that even if notifications are sent out, they may not reach the user if their settings dictate otherwise.

Moreover, the ability to receive notifications can also be influenced by the state of the device. For instance, if a device is on 'Do Not Disturb' mode or if the battery saver is activated, notifications may be restricted in terms of how they are delivered or presented to the user.

While network speed and device battery level, as well as app design and notification frequency, can also influence how effectively notifications are received and viewed, the specific option on user preferences and device settings encapsulates the direct user control factor that critically impacts notification delivery.

The other factors mentioned can affect the experience but do not override user preferences, which remain the primary determinant in whether a notification reaches its end-user successfully. Thus, focusing on user preferences and device settings provides the most accurate understanding of the delivery process for push notifications.