HIIT (High Intensity Interval Training) is very efficient at burning fat when doing cardio.
On the treadmill, I'll do 30 minutes with a two-minute warm up of just walking no incline, then going back and forth between walking quick pace, around (4.5) at a very high incline (15 or higher) for 3 1/2 to 4 minutes and sprinting at 8.0 or higher at no incline for a full minute every 5th minute.
On any type of elliptical or stationery bike, 20 seconds very high intensity, 10 seconds slow for four-minute sessions with a minute at normal intensity to warm up and in between the four-minute sessions. 20 minutes total, sometimes 30 minutes.
In nice weather, I go to local high school tracks and do 10 sprints. Sprint as fast as I can, walk back, sprint, walk back, with a couple minutes rest after 5 sprints. I absolutely love to be outside at the track sprinting on a nice day.