The Stacker isn't one of CM's best cases. I don't really like it, so I would go with the HAF.
Of course, seeing as you already have the Stacker, there's really no point in upgrading. The case still works fine, and has some pretty nice airflow.
Of course, seeing as you already have the Stacker, there's really no point in upgrading. The case still works fine, and has some pretty nice airflow.