Which Cloud computing service would be best for a new organization that cannot afford physical servers and networking equipment and must purchase network services on-demand?

The best choice for a new organization that cannot afford physical servers and networking equipment, and requires on-demand network services is Infrastructure as a Service (IaaS). IaaS provides virtualized computing resources over the internet, allowing organizations to rent servers, storage, and networking capabilities as needed, rather than investing in physical hardware. This model significantly reduces upfront costs and helps organizations scale their infrastructure based on current demands.

With IaaS, the organization can swiftly deploy virtual servers and adjust resources without needing to invest in the physical equipment or maintain the infrastructure themselves. This flexibility is particularly advantageous for startups or smaller businesses with limited budgets and rapidly changing requirements.

In contrast, Platform as a Service (PaaS) would provide a platform that enables developers to build applications without managing the underlying infrastructure, which may not directly address the immediate need for server and network services. Software as a Service (SaaS) delivers software applications over the internet, which would not fulfill the requirement for purchasing network services. Function as a Service (FaaS) is more narrowly focused on executing code in response to events and does not cover the broader infrastructure needs the organization might have. Hence, IaaS is the most appropriate solution for the situation described.