Editing the default layout for a content type in Panopoly I am using the panopoly distribution. What is the easiest and preferred way to edit the default layout for a content type.

I know that I can use panelizer for one page, but where should I go to edit the entire contenttype?
You're looking for the panels (node_view) page. You should be able to find it at admin/structure/pages and then look for node_view.  Edit that page and add a new variant for your content type.