To avoid having to select a slide master every time you open PowerPoint® you are able to set a master as a “Default Template”.
In order to do so please open PowerPoint®, choose a master template in the selection window and click on “Default Template”. A presentation with the selected template will now open automatically when you launch PowerPoint®.
Should you later want to set a different master as a Default Template or to revert the Default Template please click on “New” in the empower ribbon. You can change all required settings in the selection window via the button labelled “Default Template”.