Traditional long-duration cardio sucks for fat loss, period. I'll save you the long dissertation and give you the cliff notes version of the science behind why the majority of your training should be anaerobic (strength training/interval cardio) vs. aerobic (traditional cardio) in nature:
The physique transformation process is more complicated than the simple calories in vs. calories out theory. The real keys are to use your diet and exercise protocols to elevate your resting metabolic rate and manipulate your anabolic, lipolytic hormones and enzymes. Strength training has a much more powerful effect on these processes than aerobic training.
Many who focus on just calories and the "slash and dash" mentality end up with destructive patterns – extreme calorie cuts and/or excessive aerobics. This sets off an alarm state in the body where the body sheds muscle tissue to lessen energy demands and stores/hoards body fat as a survival response. Once this physiological state is reached, it becomes impossible to lose any more fat no matter how many calories you cut or how much aerobic work you try and add. What you end up with is someone who's on starvation level calories and performing excessive exercise, yet is still flabby.
Muscle loss due to excessive aerobics drastically lowers the resting metabolic rate and inhibits natural hormone production. When this type of person goes back to even just normal, healthy calorie and exercise levels, they gain all of the weight back plus a few extra. This generally results in a vicious cycle of huge swings in body weight and appearance. Whether it's housewives following fad diets or bodybuilders alternating between competition shape and off-season obesity is irrelevant – it's still yo-yo'ing. Sometimes the damage to the metabolism and hormones becomes so great over time that it's irreversible without medical intervention.
The calories burned during an exercise session are relatively small compared to the amount burned the other 23 hours of the day during the recovery process (at rest). Most fat oxidation occurs between training sessions, not during. As such, your workouts should primarily be geared towards building muscle and boosting the metabolism, not "burning fat."
After a workout, strength training raises the metabolic rate (the after-burn effect) for longer periods of time than cardio – up to 48 hours. This is because all of the steps involved in the recovery process from strength training (satellite cell activation, tissue repair, protein synthesis, etc.) require energy/calories.
Aerobic workouts elevate cortisol levels. Long sessions can lead to excessively high levels, and too frequent sessions can lead to chronically elevated levels, neither of which is good for body composition enhancement. Cortisol can force the body to break down its own muscle tissue, convert it to glucose, and use it as fuel. It also leads to increased fat accumulation, especially around the midsection.
Strength training raises cortisol levels, but it also raises testosterone and growth hormone – potent muscle building and fat burning hormones that offset cortisol. The net hormonal effect (assuming proper dietary support) is protein synthesis or lean muscle gain.
The body burns predominantly fat during cardio. As a result, the body adapts by up-regulating the enzymes that store body fat. The body burns predominantly glucose/glycogen during strength training. As a result, the body adapts by up-regulating the enzymes that store muscle glycogen.
Strength training has more powerful, positive nutrient partitioning effects than cardio, meaning nutrients are diverted more towards muscle cells (where they can be used to build or maintain lean muscle tissue) and away from fat cells where they can be stored.
There are certain "intermediate" muscle fibers that can take on the properties of either slow-twitch or fast-twitch muscle fibers, depending on different modes of exercise. Endurance-based training leads to the conversion of those fibers into slow twitch fibers. Strength training leads to the conversion of those fibers into fast twitch fibers. The latter is the more desirable result for physique enhancement because fast twitch fibers have the greatest potential for hypertrophy. This process is what firms and shapes the body, boosts metabolic rate, and leads to increased fat burning even at rest.