An update which is going to make few things easier when working with virtual machine in the Azure portal has been deployed.
You can now get the operating system running on the VM directly from the portal.
Connect to your Azure portal (https://portal.azure.com) and reach out the Virtual Machines blade to select the VM you want to check the OS
Then in the virtual machine overview blade you can get the operating system as well as the SKU/size
And you can also add the Operating System and/or Size properties in the columns by using the Edit colums