How to get most recent commented post above new submitted post in WordPress?

Question

Give it a try works perfect for me what it is doing query get the all the posts with a left jon with comments table so when a post has comment then it also has the comment_date if no comments posted on the post then in result set it will be null so i have merged the comment_date with post_date so which post has the greater date (for comment_date or post_date) it will first and so on

SELECT p.*,
(CASE WHEN c.comment_date IS NULL THEN p.`post_date` ELSE c.comment_date END) order_column
 FROM `wp_posts` p
LEFT  JOIN `wp_comments` c  ON (p.ID = c.`comment_post_ID` ) WHERE p.post_type="post" AND p.post_status="publish"
GROUP BY p.ID
 ORDER BY order_column   DESC

For displaying the posts you have to first get the results by defining the WP’s global variable for the database interaction i.e $wpdb

<?php
global $wpdb;
$results = $wpdb->get_results("    SELECT p.ID,
    (CASE WHEN c.comment_date IS NULL THEN p.`post_date` ELSE c.comment_date END) order_column
     FROM `wp_posts` p
    LEFT  JOIN `wp_comments` c  ON (p.ID = c.`comment_post_ID` ) WHERE p.post_type="post" AND p.post_status="publish"
    GROUP BY p.ID
     ORDER BY order_column   DESC LIMIT 20"); 
?>

HTML

<?php
foreach ($results as $id) {
  $post = &get_post( $id->ID );
  setup_postdata($post); ?>
  <p><a href="https://wordpress.stackexchange.com/questions/105534/<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></p>
  <?php
} ?>

Hope that is what you were looking for