PDO connection properly

How is the correct form to set up a PDO Connection class properly?

 

To lazy to do a simple search?
http://php.net/manual/en/book.pdo.php
http://php.net/manual/en/pdo.construct.php

 

Can you explain me:
Case 1
====

<?php
class ConexionDB extends PDO {
    public function __construct () {
        try {
                parent:: __construct('mysql:host=localhost;dbname=test;charset=utf8', 'root', 'keys');
                parent:: setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            } catch (PDOException $err) {
                    die ('There is a Error in DB');
        }
    }

    function __destruct(){
    }
}
?>

PHP:

In other file.php

$query = "SELECT * FROM prueba";
       $BD = new ConexionDB();
       $recordSet = $BD->prepare($query);
       $recordSet->execute();

PHP:

Case 2
====

class connect_pdo
{
    protected $dbh;
    public function __construct()
    {
        try {
            $con = new PDO('mysql:host='.$db_host.'; dbname='.$db_name, $db_user, $user_pw); 
            $con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
            $con->exec("SET CHARACTER SET utf8");
        }
        catch (PDOException $err) { 
            echo "harmless error message if the connection fails";
            $err->getMessage() . "<br/>";
            file_put_contents('PDOErrors.txt',$err, FILE_APPEND);
            die();
        }
    }
    public function dbh()
    {
        return $this->dbh;
    }
}

PHP:

In other file.php

$con = new connect_pdo();
$con = $con->dbh();

PHP:

What is the diference between Case 1 and Case 2, and what is the more safe connection class?