Which solution would maintain the full management responsibility with the company's IT team without reducing their workload?

Choosing an on-site solution allows the company's IT team to retain full management responsibility over the systems and infrastructure, which aligns with the need to maintain control without reducing their workload. In an on-site environment, the IT team is directly responsible for every aspect of the IT infrastructure, including hardware, software, network management, and security protocols. This ensures that they handle all operational aspects according to the company’s specific standards and policies, leading to better responsiveness and customization.

In contrast, SaaS (Software as a Service) provides applications hosted by a third-party provider, which means management responsibilities are shared, leading to a decrease in direct control for the IT team. PaaS (Platform as a Service) offers a platform that developers can use to build applications without managing the underlying hardware and software layers, which similarly reduces the IT team's hands-on management role. IaaS (Infrastructure as a Service) gives access to virtualized computing resources over the internet, but still relies on third-party providers for infrastructure management, thereby shifting key responsibilities away from the internal IT team.

Thus, the on-site solution is the best choice for maintaining full responsibility while keeping the current workload intact.