Without a doubt when it comes to getting lean in a hurry, NOTHING can compare to challenging sprint workouts that emphasize your fast twitch muscle fibers over your slow twitch. Sprints are hands down the best way to incinerate stubborn fat stores without tapping into your existing muscle mass like long steady state cardio does.
When most people are trying to get lean fast they assume that long bouts of cardio on the treadmill are the best recipe for fat loss success, but in reality all you need to do is 2-3 short sprint workouts per week to burn fat at superhuman speed while simultaneously skyrocketing your fat loss hormones testosterone and human growth hormone.
Long cardio sessions that are between say 30 - 60 minutes are not ideal for fat loss and leaning out because of the compound effect of what is happening in your body. Long bouts of cardio are going to lower your testosterone and human growth hormone levels as well as causing a massive spike in your hunger hormones. They also can easily cause muscle loss if you are in a calorie deficit.
The advantage sprints have over cardio is they not only help you keen and in some cases even build muscle when you are in a deficit, but they keep your insulin and cortisol regulated properly helping you lean out even more. Long cardio sessions not only can cause a spike in your hunger hormones, but they also raise your cortisol levels which signals to your body to store fat.
Sprinting workouts can be as simple as running as fast as you can for 10 seconds and doing 8-10 intervals with 45 seconds rest between sprints. If you want an extra challenge try running your sprints on a hill!