Query to get the author who having maximum number of post (custom post type)

You can try with the following query, where the author data as well as the post count can be retrieved.

$sql = "SELECT SQL_CALC_FOUND_ROWS wp_users.ID,post_count FROM wp_users RIGHT JOIN (SELECT post_author, COUNT(*) as post_count FROM wp_posts WHERE ( ( post_type="custom-post-type" AND ( post_status="publish"  ) ) ) GROUP BY post_author) p ON (wp_users.ID = p.post_author) WHERE 1=1 ORDER BY post_count DESC";

$result = $wpdb->get_results($sql,OBJECT);
print_r($result);