Weight Loss Contest
To answer your question let me begin by saying the only way to gain weight is to eat more calories than you burn and the only way to lose weight is to eat less calories than you burn. Lifting weights burns calories as does any form of exercise whether it be cardio or strength based and has nothing to do with weight gain.
To lose weight you have to create what is known as a calorie deficit. This simply means you have to eat less than you burn. If you eat 500 calories less than you burn every day you will have a weekly calorie deficit of (7x500)= 3500 calories and you will lose exactly one pound every week. Create a daily calorie deficit of 1000 calories and you will lose (7x1000 = 7000 calories) 2 pounds per week. FYI, our new Workout Manager has a built in weight loss forecaster that will do this math instantly for you.
There are two parts to the weight loss equation: 1. Calories consumed and 2. Calories burned. To maximize weight loss you need to work both sides of the equation and that is the problem with weight loss contest - they encourage unsafe practices in many cases.
Okay, enough background about weight loss. You wanted to know about whether STS would be a wise choice. In the long term absolutely STS is the way to go as it will help to build lean muscle mass that will increase your body's metabolic rate (BMR) helping you burn more calories even when your sleeping. I know when you see "builds lean muscle mass" it paints a vision in ones mind of looking like the Incredible Hulk, but that is not the case. It is very difficult for even a young male to add more than a few pounds of muscle in an entire year and for women much less is possible. When you consume more calories than you burn the calories are usually stored as fat in your body, not as muscle. When a person says their legs got bigger from weight training it is not from the increased lean muscle mass, but instead from eating too much and the resulting increase in body fat that is the problem.
But back to your contest. STS is also a good calorie burner in the short term, but there are cardio only workouts that will certainly burn more calories. So if to win a weight loss contest is your "only goal" then cardio only will give you the most bang for your buck in the short term if you can stick to your own program. If long term weight loss, looking and being healthier are your goals then I feel nothing beats STS. Still, the difference in calorie burn between STS and a very hard cardio workout is only about 200 to 300 calories per workout.
Since you only do STS three times per week you also can and should add cardio workouts to your STS program and thus the calorie difference between doing a cardio only and a combined STS/Cardio routine is not very significant. So you may want to consider doing both. STS has the advantage of making and helping you stick to your exercise program. Most people fail an exercise program because they are not consistent with their workouts. Our New Free Workout Manager (coming soon) can also help you be accountable and stick to your weight loss program. Studies show that people who record their results are more successful with their weight loss than those who don't.