If you want to display most commented post or most popular post on your blog, you can display that using following code.

WordPress Popular Post or Most Commented Post without a Plugin

<h2>Popular Posts</h2>
<ul>
<?php $result = $wpdb->get_results("SELECT comment_count,ID,post_title FROM $wpdb->posts ORDER BY comment_count DESC LIMIT 0 , 5");
foreach ($result as $post) {
setup_postdata($post);
$postid = $post->ID;
$title = $post->post_title;
$commentcount = $post->comment_count;
if ($commentcount != 0) { ?>
<li><a href="<?php echo get_permalink($postid); ?>" title="<?php echo $title ?>">

<?php echo $title ?></a> {<?php echo $commentcount ?>}</li>
<?php } } ?>
</ul>