$pp = new WP_Query(array(
'post_type' => array( 'post', 'custom_type' ),
'orderby' => 'comment_count',
'posts_per_page' => 4
));
$pp = new WP_Query(array(
'post_type' => array( 'post', 'custom_type' ),
'orderby' => 'comment_count',
'posts_per_page' => 4
));