According to this article, and consistant with what I've learned using the iLipoXcell device for body sculpting and fat loss, achieving a heart rate of 65 percent of max (for your age) is the best method of burning fat stores for energy. Greater intensity exercise seems to reduce appetite as well.
From the NY Times Well Section:
Ask Well: Exercise and Weight Loss
By GRETCHEN REYNOLDS
July 28, 2014 3:05 pmJuly 29, 2014 2:21 pm
Credit Jacob Silberberg for The New York Times
Is weight loss truly greater (for the same time expended) when exercising at moderate (say, 60 percent of maximum capacity) versus more intense levels (85 percent of maximum capacity)?
Actually, the reverse is true. Minute for minute, you will expend more energy and therefore burn more calories if you exercise intensely rather than moderately. In other words, running for 30 minutes uses more calories than walking for that same half hour.
I suspect, though, that you refer to the widespread belief that you burn more fat when you exercise moderately compared with strenuously, which is true. During intense exercise, the body needs rapidly combustible calories from carbohydrates, but when you’re moving at a relatively unhurried pace, the energy demands are lower, and the body can turn to slower-burning fat for fuel. According to a 2009 study in The Journal of Strength and Conditioning Research, exercising at an intensity of about 65 percent to 80 percent of your maximal heart rate, or a pulse rate of about 105 to 130 beats per minute, maximizes the amount of fat that you burn during a workout but requires less overall caloric expenditure per minute than tougher exercise.
Intense exercise may also quell later appetite, unlike gentler exercise. In an interesting study from earlier this year, men who rode stationary bicycles intensely for 30 minutes consumed far fewer calories afterward than when they rode moderately for 30 minutes and had lower blood levels of the hormone ghrelin, which is known to stimulate appetite.
Still, the keys to losing weight with exercise are common sense and restraint.
“It all comes down to energy balance,” or calories in and calories out, said Edward Melanson, a professor at the University of Colorado School of Medicine in Denver, who has conducted many studies of exercise and weight loss. Most of us will burn only 200 or 300 calories in a moderate 30-minute exercise session, he said, adding, “You replace that with one bottle of Gatorade.”