Best way to change the Single Template for a specific Category

What is the best way (performence & code structure) to create a custom template for a WordPress Post, which belong to a specific category? I realized that you can’t just create single-catname.php.

So far i tried two ways to change the template. But wich one (or another one) ist the best?

1. Added to functions.php

    function get_custom_cat_template($single_template) {
    global $post;
    if ( in_category( 'movies' )) {
    $single_template = dirname( __FILE__ ) . '/single-movies.php';
    }
    return $single_template;
    }
    add_filter( "single_template", "get_custom_cat_template" ) ;

2. Put the following Code in to single.php (instead of all other code) and create also a single-template.php (with the code from the single.php) & a custom single-movies.php

    <?php        
    if(has_term('movies', 'category', $post)) {      
    get_template_part('single-movies', 'movies');
    } else {
    // use default template file single-template.php
    get_template_part('single-template');
    }
    ?>