Based on David's answer, I wrote the following script that combines the two lists of VMs:
Switch-AzureMode -Name AzureServiceManagement#ResourceGroupName will be blank for these$classicVms = Get-AzureVM | select Name, ServiceName, ResourceGroupNameSwitch-AzureMode -Name AzureResourceManager #ServiceName will be blank for these$armVms = Get-AzureVM | select Name, ServiceName, ResourceGroupName $allVms = $classicVms + $armVms$allVmsWhen you run this, you'll get a warning that Switch-AzureMode is deprecated.
WARNING: The Switch-AzureMode cmdlet is deprecated and will be removed in a future releaseThe deprecation is part of a breaking change. You can read the details here: Deprecation of Switch-AzureMode.
