You can always use a selection factory to control the options.
If you do that one you get full control of your drop-down but a little more work. You can use
var repository = ServiceLocator.Current.GetInstance<PageTypeRepository>();
Use the list method to generate the options
Then either set default value like you do or set it in factory. It's hidden in the metadata object and called initial value.
Not sure how to go about setting a default value for a PageType property
The PageType property provides drop down list of all the page types.
How do you have one selected by default, or force the dropdown to only show a subset of pagetypes/