I would like to change the default settings for all podcasts.
I know you can edit each one of them individually, but I would like to change the default for all to "Download All" and keep "All episodes".
iTunes 11.1.2 adds a new dialog for changing podcast settings. Select Settings and select Defaults... to change the default podcast settings.
Try selecting NONE of the podcasts. Click on an empty spot in iTunes and then change "Settings..." That should change the defaults for podcasts you subscribe to in the future.