Question about excerpts in postformat

I recently finished two sites which use <?php the_excerpt(); ?> in postformat.php, but I'm having conflicting behavior on them.

One site creates an excerpt from content if excerpt window is left empty, but gives priority to content in the excerpt window when filled. The other simply ignores all content and only looks at the excerpt window. So when the excerpt window is left empty, no content shows in postformat.

Which of the two is the expected behavior of <?php the_excerpt(); ?>?