It depends on your requirement. Let's discuss one by one.
Nova-network is the simplest networking solution, which has limited capabilities but is available on any OpenStack deployment without the need to deploy any additional components.
When a new murano environment is created, murano checks if a dedicated networking service, for example, neutron, exists in the current OpenStack deployment. It relies on the Identity service catalog for that. If such a service is not present, murano automatically falls back to nova-network. No further configuration is needed in this case, all the VMs spawned by Murano will be joining the same network.
If neutron is installed, murano enables its advanced networking features that give you the ability to avoid configuring networks for your application.
By default, it creates an isolated network for each environment and joins all VMs needed by your application to that network. To install and configure the application in a newly spawned virtual machine, murano also requires a router to be connected to the external network.
Hope this will help you.