You can enable the Enhanced Editor to be your default editor by using the WikiTree drop-down menu and choosing the Settings option. Under Tools, set the Text Editor radio button to "Use Enhanced Editor" (or with line numbers, if desired). Make sure to click the "Save Settings" button at the bottom of the page to save your choice.
You may want to review your other settings while there. And again, don't forget to click the "Save Settings" button at the bottom to save your choices.