php html date - controlling twine concatention

a doubt opposite methods outputting html php; opening differences between these:

method 1 - non-static concatenation

$html = '';
$html .= '<ul>';
for ($k = 1; $k < = 1000; $k++){
    $html .= '<li> list vigilant #'.$k.'</li>';
}
$html .= '</ul>';
echo $html;

method 2 - cost buffering

ob_start();
echo '<ul>';
for ($k = 1; $k < = 1000; $k++){
    relate '<li> list vigilant #',$k,'</li>';
}
echo '</ul>';

i think opening strike continuously modifying swelling variable; correct?

cheers!

thanks garyf, nonetheless i don't wish an answer settlement - doubt performance. there seem opposite opinions / contrast faster, since there an supposed answer yet.