Conventional wisdom is run longer to burn more calories. However, many believe that more calories and FAT are burned after the exercise session due to recovery requirements and hormonal changes brought on by intense exercise, therefor running faster for shorter time periods may actually result in more fat and weight loss for many individuals. Also, there is some evidence that long-duration low-intensity cardio sessions stimulate release of the hormone cortisol which signals your body to store fat (to supply energy for the next long-duration exercise session you body assumes it will be called upon to execute in the near future). So for many, Tabita type (20 seconds sprint, 10 seconds rest, repeat 8 times), HIIT type(10-20 seconds sprint, 60-120 seconds rest, repeat 8 times) or 20 minutes at the fastest pace you can run (with some uphill stretches) result in the maximum fat loss possible with maximum cardiovascular benefit in the shortest time with the least chance of over use injury over the long term.