i think swimming is better than running as you use more energy and all parts of your body. It also increases flexibility and strength.
But running is more convenient for most people. I prefer running coz i can just go out running whenever i want, whereas i'd have to walk 20 minutes to the nearest swimming pool and i have eczema so the chlorine water really irritates my skin.
So yeh, going running as often as you can is probably the best way to lose fat. And I think it's better to run for longer periods of time. I'm trying to jog 6.5 miles each Friday as well as 1.5 miles a few days of the week after school. The hardest part of running is forcing yourself to get out there and keeping at your routine. So far i've done four fridays in a row. I hope i can carry on through the summer or maybe do even more.
also, the first time i ran for 6.5 miles felt like such an achievement. It would be really nice to run a marathon one day. I know i'd have to train a lot more, but i'm going to strive to improve.
Run, swim, play sports, lift weights, ect. Cardio burns a lot of calories, but weightlifting if you have intense workouts burns almost as much. Also, weightlifting builds lean muscle, the base of a good metabolism. Basically just get off your ass.
Paintballing burns a lot of calories because of the adrenaline. Not to mention it's fun as hell.