You have to decide whether you want fat burning exercises or calorie burning exercises:
1) For low-intensity endurance cardio, like road cycling and running a semi-marathon, your body will specifically tap into fat. Not necessarily body fat, it will actually use mostly dietary fats, so it's as useful as it sounds.
2) With High-intensity interval training, you can burn a larger amount of calories in a shorter time, but those calories will come mostly from carbs instead of fat. Then it will affect your total daily calorie balance and you will lose fat during the rest of the day.
In any case, just keep in mind that the number of calories you can burn that way is usually relatively small compared to how many calories we can easily cut from our diet (except for vegetarians), and it's also much more difficult to evaluate precisely.