Aerobic exercise is helpful in control and prevention of diabetes, hypertension, and raises HDL cholesterol (the 'good' cholesterol). By aerobic, we mean exercise that involves continuous activity and makes you breathe harder. This sort of exercise burns calories and thus aids in weight control.
You should choose an exercise that is suited to you; if it is fun, convenient, and compatible with your physique you will be stick with it. Dancing, commuting by bicycle or on foot (half the time you spend exercising was going to be spent in your car), pool aerobics (the water supports your weight so its easy on knees, hips and ankles) are all good exercises that meet specific needs.