The best type of aerobic exercise is the one that you enjoy the most. It is hard to find the time and the energy to begin an exercise program and it will only become more difficult if you force yourself to do something that you don't like to do. Experiment with different activities, machines, or classes until you find something you enjoy and can look forward to doing on a regular basis. If it is at all possible, make sure that you incorporate some weight bearing activities such as walking or jogging into your routine to help your bones.