NickFit saidMy opinion when it comes to cardio is that anything that gets your heart rate up into the levels where you are burning fat is fine, and the most important thing is that you pick something that you like doing.
Lots of people fail because they hate it and find it boring so hard to stick to. So whetever you do, make it something you enjoy - whether that's treadmill, rowing machine, mountain biking, vigorous sex in a variety of athletic positions, or pole dancing.
This sounds similar to what a personal trainer friend recommends in a booklet that he wrote for the clients at his gym. He says that the ONLY way to burn fat is through aerobic cardio. He has several easy rules of thumb to define aerobic vs anaerobic exercise. With aerobic cardio, breathing should be steady and audible, but only mildly labored. (You should be able to carry on a conversation.) The exercise should be tiring, but not un-pleasurable. On a scale of 1 - 10, with 1 being nearly no effort, and 10 being extreme effort, you don't want to exceed a 7.
The exercise should be steady and rhythmic, not start, stop, start, stop. Try to maintain your target heart rate for at least 30 minutes. Your target heart rate can be calculated by subtracting your age from 220, then multiplying that number by 75%. That number will roughly estimate what your heart rate should be while performing the exercise. Perform aerobic cardio at least four times each week.
Anything more vigorous will likely become anaerobic exercise that burns glucose/glycogen (carbohydrate stores). Anaeorbic exercise is considered stress to the body, releasing the stress hormone cortisol. Cortisol stores fat.
I can't personally vouch for the accuracy of this advice, but I can say that this particular personal trainer is pretty damned hot, so, if he's following his own advice, it must work!