Researchers at Duke University followed overweight and sedentary participants for 8 months. Participants exercised with aerobics, strength training, or a combination of the two. At the end of the study the cardio group lost the most weight.
The strength training group gained weight from increased muscle mass but did not lose even 1 pound of fat mass despite exercising 47 minutes more each week.
The group that combined cardio and strength training lost some weight, had the best improvements in body composition by losing the most fat, and increased muscle mass.
Cardio burns more calories per minute compared to strength training so it is beneficial for reducing weight. Strength training is important too though, especially for maintaining lean muscle mass (which impacts metabolic rate), improving bone mineral density, and proper body mechanics for daily activities.
For the best benefit start with a warm-up and then move into strength training followed by cardio. The American Council on Exercise found this can drive heart rate higher during the cardio session which helps burn more calories.
It is recommended to do cardio exercise at least 30 minutes 5 days per week, although 60 minutes is best for weight management. Strength training should be at least two or more times per week with all major muscle groups being worked to volitional fatigue. Brisk walking counts as cardio, but greater benefit is seen with more vigorous activity.