Running and hiking are best if you want to slim down.
Which is the best sport to slim down?
The best sport to slim down is the one you enjoy the most! You're not going to want to practice a sport you don't enjoy, so pick a sport that you can really get into if you want the weightloss to be fun and effortless.
Having said that, here are some of the top sports in terms of calorie burn:
-running
-rock climbing
-swimming
-cycling
-boxing
-racquetball
-basketball
-rowing
-tennis
-cross country skiing
-ice skating
Swimming is my favorite cardio exercise personally, Its fun and works your entire body. Just find something you enjoy doing - then it wont seem like a chore.
What about bicycling?