Ettercap is highly effective for ARP poisoning, which is a technique used to intercept the traffic between two hosts on a network. Its ability to conduct ARP spoofing allows a penetration tester to reroute traffic through their own system, permitting them to sniff packets or even modify them on-the-fly before forwarding them to the intended recipient. This makes ARP poisoning the best scenario for making use of Ettercap's capabilities, as it is designed specifically to handle such types of attacks efficiently. Other options, like creating a reverse shell or code signing, are unrelated to Ettercap's core functionality and thus are incorrect in this context.