Give me 10-15 minutes of crazy, HIGH INTENSITY, intervals on a treadmill or a set of stairs any day. Even better, stagger your sprints into your weight training, and BOOM. My clients can attest, we do not believe in the word comfortable when it comes to cardio. If you want to torch fat, add years to your life, and see results, step it up, and "SPRINT."
That doesn't mean you're going as fast as you can for as long as you can, a true sprint should be at about a minute or less in length, with your legs going as fast as you possibly can. Don't let that treadmill tell you what to do, you're the boss, and you're going to make that treadmill your bitch!
Check out the feature from Men's Fitness below, in an article about how to "Burn Fat Faster," and some of the top benefits of sprinting, and why you need to pick up the speed.