As an exercise physiologist, I believe that there is really no one type of Aerobic exercise that is best for everyone, however, for it to be considered aerobic and for you to get all the calorie burning benefits that come along with it, the exercise must meet certain criteria:
It should be done a minimum of 30 minutes at least 3 to 5 times a week.
It should use large muscle groups over a sustained amount of time to get you heart rate up to 65% of your maximum target heart rate or at minimum reach the cardiovascular goal that your doctor or exercise physiologist sets for you.
It needs to be something that you enjoy so that you will stick with the program.
Any exercise program should be maintained over a long period of time. Benefits increase as the program continues. It is said that it takes at least 4 weeks for changes to begin, 8 weeks for you to notice and 12 weeks for everyone else to notice. Most people fail in their program in the first 4 weeks, so if you can push past that point to 8 weeks, you will begin to notice a big enough difference that you will be able to get motivated to continue. Additionally, good nutrition choices will help to increase the benefits of any exercise program in terms of both, appearance and health benefits.
One final note is that some studies have shown that adding interval training to your aerobic program once or twice a week increases the calorie burning benefit, but it should be noted that too much interval training can lead to injury so it should be done under supervision of your doctor or exercise physiologist.