If you want to lose wt, exercise alone is not likely the answer. In fact if you are obese, you may be more susceptible to injury. Here's why. In order to lose one lb, you must burn 3500 cal. When you walk one mile you use 100 calories. So to lose one lb, you must walk 35 miles. One serious hour in a gym can burn 300 to 400 calories. So you need about 10 of those sessions to lose one lb.
Now lets look at the food side. One medium coke will add about 300 calories. In one year this could be stored as 25 lbs of fat. One coke can easily negate a heavy workout session at the gym.
My recommendation is you must diet to lose weight but a lifestyle change that includes exercise will put you on a path to achieving optimal health.