In WordPress dashboard, the default editor is the “Visual Editor”. It is probably the editor that most people enjoy, but personally I prefer using the HTML editor. If you’re like me you’ll probably like this tip which will make the HTML editor as the default.
Simply paste the following code on your functions.php file, save it, and you’re done!
add_filter('wp_default_editor', create_function('', 'return "html";'));
Credit: WP Snippets.