The best fat burning method is moderate intensity aerobics. 45 minutes is sufficient, 3-5 times per week. Make sure you're getting in enough resistance training too. You may want to do your weights first, so you're not spent up after cardio. When you do your cardio too intensely you will burn some muscle. Anaerobic cardio is difficult to recover from too.
I really depends on what your goals are. When I was trying to lose a bunch of fat a couple of years ago, I was doing cardio 5-6 days a week with some serious intensity. What happened was eventually I started burning some muscle, because I saw my bench go down. That was due mostly to the intensity of the cardio I was doing. Spinning classes 2-3 times per week, and 2-3 days on the eliptical trainer for 45-60 minutes. I learned from that. Currently, I'm cutting and doing cardio on seperate days from my weights, with the exception of Thursdays which I train weights in the morning, and teach 2 spinning classes at night. Other than that I do cardio on 2 other days with no weights, and weights 3-4 days on separate days. Currently, I'm at 200 lbs at about 7 or 8% at 5'11".
Hope this helps.