How to make the "Don't save" or "delete" options the default?
The options you want to make the default, are the options that are the most likely to cause data loss, and so they are not the default for a reason. However, you mentioned quitting using the ⌘Q key, so you’re not afraid to use keyboard shortcuts.

I mention this because the Mac OS usually allows you to select a button in a dialog by hitting ⌘ and the first letter of the button’s text. In the ‘Delete’ or ‘Don’t save’ case, this would mean you can dismiss the dialog and not save by hitting ⌘D. For ‘Revert’, hit ⌘R.

It’s not as convenient as ⌘Q and Enter, but it’s still two keystrokes. And without opening you up to potential data loss by default.