Firstly, you have to address your nutrition.
YOU CANNOT OUT-TRAIN POOR NUTRITION.
It's so easy to consume, in one meal, more calories than it is possible to burn off in one day. If you are eating too many calories, no amount of cardio will burn off the excess calories. let alone your fat stores.
When carbohydrates are consumed, they are turned by your body into glucose. Once you have eaten a certain amount of carbohydrate, your body turns the glucose to glycogen for storage, it gets stored in your muscles and your liver. Once your liver is overloaded with glycogen, your body ceases to release leptin, which is the hormone responsible for telling your brain you are full. And once your muscles and liver stores are full, the remainder is stored as fat.
So, it stands to reason that the more muscle you have, the more potential you have for glycogen storage, meaning less is turned to fat in the first place. Also, muscle takes more calories to maintain than fat does, so again, it stands to reason that the more muscle you have, the more calories you will burn.
So if you want to become a fat burning machine, you need to build muscle. That does not necessarily mean bulking up, it simply means changing the ratio of fat to muscle. Less fat, more muscle rather than the other way around.
The best way to do this is with resistance training, or weights. Not cardio.
There is evidence to suggest that vast amounts of cardio can actually be counter-productive in the quest to burn fat. Your body becomes used to the exercise very quickly and allows fat to be stored more effectively for use when you are in the so-called fat-burning zone.
That isn't to say that cardio is bad for you - it is always good to be more active - just that it won't help you in the fight to lose fat.
The two best things you can do to lose fat are:
1 address your nutrition
2 lift some weights.
If you still want to do cardio, that's brilliant. The best thing you can do is to go for lots of long walks. It's a natural, low-impact way to work your heart and lungs and joints. Endless hours on the cross trainer or treadmill are not only mind-numbingly dull, they are virtually pointless. if you want to do some cardio in the gym, go for the rower as you get a full body workout at the same time, killing two birds with one stone.
On the matter of running, it's an addictive thing and people do it for the buzz. personally, I'm not a fan. I don't believe it is natural for any animal to run for prolonged periods of time and if I have to choose between an hour in the gym and an hour's run, I'll always opt for the gym. having said that, if you enjoy running and want to get the most from it, try turning your run into a fartlek session or interval session - much more natural than a straight run.