A hybrid cloud model would be the most suitable option as it combines the features of both private and public clouds. It allows sensitive data to remain on-premises in a private cloud, addressing the regulatory requirements, while leveraging the scalability of public cloud services for collaboration tools and email. A private cloud alone would not offer the same level of scalability and resource availability as a hybrid model, and a public cloud does not provide the same level of control over sensitive data. A community cloud involves sharing infrastructure between organizations with common interests, which is not specified as a requirement in this scenario.