It doesn't matter. If you stay in the 'fat burning zone' during a cardio session, then you're just going to use more carbs later in the day. If you use more glycogen during a cardio session, you will use more fat later in the day. http://alanaragon.com/myths-under-the-microscope-the-fat-burning-zone-fasted-cardio.html
Slowly but surely I'm starting to realize that everything I learned in my high school PE/weight lifting classes is wrong.
