Azure Virtual Network Peering, as it enables you to connect isolated virtual networks seamlessly, ensuring secure and isolated communication between different environments without the need for gateways or public internet.

Azure Virtual Subnets, which allow for the creation of isolated network segments within a single virtual network, but may not provide the level of isolation required between distinct environments.

Azure VPN Gateway, which provides secure site-to-site connectivity over the public internet, but may introduce latency and does not offer the same level of isolation as private connections.

Azure ExpressRoute, offering dedicated private network connectivity that bypasses the public internet, ensuring high security and isolation, but at a higher cost and with less flexibility for scaling.

A combination of Azure Virtual Network Peering and Network Security Groups (NSGs) to not only isolate the environments but also to finely control the traffic between them, ensuring compliance and security.