PHP - exit or return which is better

Question

Case I:

<?php
if ( $fileSize > 100 )
{
   $results['msg'] = 'fileSize is too big!';
   echo json_encode( $results );
   exit();
}

Case II:

<?php
if ( $fileSize > 100 )
{
   $results['msg'] = 'fileSize is too big!';
   exit( json_encode( $results ) );
}

Case III:

<?php
if ( $fileSize > 100 )
{
   $results['msg'] = 'fileSize is too big!';
   return( json_encode( $results ) );
}

In the PHP script, if the $fileSize variable is larger than 100, I stop the script;

Which of the three (3) options above is the best?