I've found for me there is a threshold: If I eat 1600 cal or less per day my body will go into weight loss mode and start catabolizm. If I eat 1700 or more a day, no matter how much I work out, my body olds onto everything it's got. So, I've learned that eating well is VERY important to losing fat.
That and cardio! I am in medical school now, and I was so excited when during our lecture on exercise physiology our professor told us that cardiovascular exercise is key to buring more calories and losing fat. Resistance training, while it will make your muscles strong and tone your body, will not get rid of much fat. But why Cardio? Well, it increases the number of mitochondia, increases the number of mitochondial enzymes and increases the number of capillaries to your muscles. All of this improves your efficiency in using Oxygen and nutrients to generate ATP (energy), and you burn more calories doing cardio. People like to over estimate how much extra muscle burns calories during rest. 2 extra pounds of muscle will only increase your caloric needs by 20kcal/ day. That's nothing! That being said- I think resistance training is important, especially to combat natural muscle atrophy.
That's all I've got for you now. I hope it helps.
-RR