Returns the active transform. (The one shown in the inspector).

class SelectionActiveTransform extends ScriptableObject {
    @MenuItem ("Example/Duplicate at Origin _d")
    static function DuplicateSelected() {
        Instantiate(Selection.activeTransform, Vector3.zero, Quaternion.identity);
    }
    //The menu item will be disabled if nothing, is selected.
    @MenuItem ("Example/Duplicate at Origin _d", true)
    static function ValidateSelection() {
        return Selection.activeTransform != null;
    }
}