If you want the time you spend exercising to have the biggest impact on the number on the bathroom scale, then start running or cycling.
Why? Aerobic exercise, which includes running, jogging, power walking, swimming, cycling, rowing and jumping rope, is more effective than resistance training at losing weight and burning fat, according to a study from Duke University in Durham, North Carolina. HealthDay News reports that while resistance training has many benefits, including improving blood sugar control, it has not been shown to have an effect on fat reduction. If you are short on time, focus on aerobic exercise as the best way to lose weight and burn fat. Use resistance training when you have time to help maintain muscle strength, which becomes more important as you age and lose muscle mass.