High Intensity or Low Intensity aerobics?
If you decide to not to use intervals as your calorie burning exercise of choice, then LOW intensity, moderate duration is the way to go. Performing high intensity cardio for anything more than a short duration (especially around the lactate threshold), will result in more muscle breakdown that it will be worth in energy expenditure. 30-40 minutes, 3 times a week is a good point to start and adjust from.