An administrator needs to repeatedly scan a very large network with thousands of hosts, what is the best way of accomplishing this very quickly?

Nessus is a credentialed vulnerability and configuration scanner that performs deep per-host checks - it is not designed for raw speed across thousands of hosts and would be far too slow for this use case.

Nmap uses the host OS network stack and is feature-rich and accurate, but its architecture does not scale to scanning thousands of hosts quickly - it is significantly slower than Masscan for large sweeps.

Masscan uses an asynchronous, stateless TCP/IP stack that bypasses the operating system's network stack, allowing it to transmit millions of packets per second. It can scan the entire IPv4 internet in under six minutes at maximum rate, making it far superior to other tools for rapidly sweeping very large address spaces. Its design is explicitly optimized for speed and scale, unlike Nmap which prioritizes accuracy and feature richness.

Hping3 is a packet crafting and testing tool used for firewall testing, tracerouting, and crafting custom packets - it has no built-in scanning engine suitable for rapidly scanning large networks.