Which layer of the TCP/IP protocol model would best correspond to the OSI/ISO model's network...

The Internet layer corresponds to the OSI's network layer. It handles the routing of packets among multiple networks.

Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 3: Telecommunications and Network Security (page 85).