Which swimming stoke burns most calories?

I've always found the freestyle stroke aka from crawl to be the most exhaustive stroke to do. I have to caution you though, swimming is generally not for losing weight becuase the cold temperatures (even in a heated pool) fool the metabolism.. it actually lowers the metabolism. What's worse is you wiil expend so much energy that you might find your caloric intake going way up.. a bad combo for weight loss. I swim 4 to 5 days a week for 1/2 mile a day for the past 1 1/2 years.. I have gained 18 pounds.. mostly muscle.. but still