Quality of Service (QoS) is the correct feature to use when there is a need to prioritize certain types of traffic, such as VoIP, over others. QoS mechanisms can classify network traffic, apply the appropriate policies, and ensure that essential services like voice receive higher priority over less critical traffic. Traffic shaping, on the other hand, is used to control the flow of data entering the network, shaping traffic patterns to prevent congestion but not necessarily prioritizing one type of traffic over another. Port security and Spanning Tree Protocol (STP) are not directly related to traffic prioritization; port security is used for securing ports against unauthorized access, and STP helps prevent network loops.