Using Transport Layer Security (TLS) ensures that data in transit is encrypted end-to-end between the on-premises systems and cloud services, preventing unauthorized access or interception of the data. TLS is the successor to Secure Sockets Layer (SSL) and is widely adopted for securing communications. The other options, SSH, L2TP, and GRE, are protocols used for different use cases. SSH is typically used for secure command-line access, L2TP is for VPN connections and doesn't provide encryption by itself, and GRE is used for tunneling rather than encryption.