A protocol analyzer/packet capture tool is the best choice for monitoring and analyzing network traffic to identify potential issues such as high volumes of unexpected traffic. This type of tool provides detailed information about the traffic, including the source and destination of packets, protocols used, and other vital details that can help identify the cause of slow response times.

Using a bandwidth speed tester would not provide the same level of detail as it primarily measures the maximum throughput of a connection. WiFi analyzer would not be appropriate either, as it is specialized for analyzing wireless network performance rather than the entire network. Lastly, an IP scanner is used to scan and identify IP addresses within a network but does not offer traffic analysis.