How to return loop contents

At times, I need to return the output of a loop (usually with WP_Query like in this example) for use in a shortcode or with a filter on the_content.

The following code that uses object buffering works, but I’ve read in other places that buffering can be inefficient. I’ve seen HEREDOC too, but I don’t see how that would work here unless I saved every template tag as a variable first (which seems inefficient again).

So my question is, what’s the best way to return the output of a loop?

<?php if ( $cms_pl_pages->have_posts() ) :
ob_start(); // start object buffering. we'll run the loop and spit out final contents.
echo '<section class="cms-pl-gallery">';
while ( $cms_pl_pages->have_posts() ) : $cms_pl_pages->the_post();
?>
    <article class="cms-pl-item clearfix">
        <?php has_post_thumbnail() ? the_post_thumbnail() : null; ?>
        <a href="https://wordpress.stackexchange.com/questions/57000/<?php the_permalink(); ?>" title="Read '<?php the_title(); ?>.'">
            <h2><?php the_title(); ?></h2>
        </a>
        <?php has_excerpt() ? the_excerpt() : null; ?>
    </article>

<?php endwhile;
echo '</section> <!-- end .cms-pl-gallery -->';
$content = ob_get_contents(); // set $content to buffered object
ob_end_clean(); // throw away the buffered object
endif; wp_reset_postdata();
return $content; // return! ?>

There are replacements that return pure strings for all parts, no need to print anything into an output buffer. I like sprintf() and would write your example like this:

<?php
if ( $cms_pl_pages->have_posts() )
{
    $content="<section class="cms-pl-gallery">";
    while ( $cms_pl_pages->have_posts() )
    {
        $cms_pl_pages->the_post();
        $content .= sprintf(
            '<article class="cms-pl-item clearfix">
                %1$s
                <h2>
                    <a href="https://wordpress.stackexchange.com/questions/57000/%2$s" title="Read %3$s">%4$s</a>
                </h2>
                %5$s
            </article>',
            get_the_post_thumbnail(),
            apply_filters( 'the_permalink', get_permalink() ),
            the_title_attribute( array( 'echo' => FALSE ) ),
            the_title( '', '', FALSE ),
            has_excerpt() ? apply_filters( 'the_excerpt', get_the_excerpt() ) : ''
        );
    }
    $content .= '</section> <!-- end .cms-pl-gallery -->';
}
wp_reset_postdata();
return $content;