It is absolutely impossible to measure how many calories the body uses during a certain workout with a heart rate monitor, let alone determine from what source the burned calories came. It’s not even an educated guess, you could also roll dice or flip some coins to determine a random number.
Furthermore, the process of regeneration often uses twice or more the amount of calories than the actual workout over the period of ~36-48 hours, this is especially true for high intensity workouts and resistance training (lifting).
First thing you probably want to do is understand that you don’t reduce bodyfat by actually burning fat as an caloric energy source. The body converts any type of food into fat anyway as long you are eating more calories (from any source) than you are using.
So what you want to do most likely is to burn as many calories as possible in the shortest amount of time. In that case, any kind of high intensity workout, e.g. HIIT or weightlifting (optimal would be a combination of both) is vastly superior to any kind of low heartrate steady cardio.
Another important aspect would be that your appearance (body composition etc) is a function of your eating habits, not so much of your training. You cannot ‘outtrain’ a bad diet.
I would start reading those wonderful articles available for free on this site, esp by Dr. John Berardi & David Barr
EDIT:some real bad spelling/grammar