best cardio exercise

Hey..
I just want to know your point of view about cardio exercise.. Just tell me one thing which is best cardio exercise..??
Running
swimming

Swimming is better than running, the impact on your joints is virtually non-existent, and it's a whole-body exercise (like running is) with resistance thrown in. On the other hand, it's a pain to go to the pool regularly, which is why I prefer bicycling. Less resistance than either, but very low impact on your joints, and for time spent (not distance) you can get as much benefit out of it as you do running, if you conscientiously apply yourself and don't slack off.

Can confirm. ^ My last HM nearly killed my knees.

My personal favorite running alternative would be jumping rope. You can go to a sporting goods store and get some with weights on each handle. It's extremely intense, provides awesome cross-training benefits, and is virtually no impact.

They're all good cardio wise... That depends on your preference. Personally, I like running. Been running for 12 years at least 5 miles 3-5 times/week outdoors when the weather is nice or on the threadmill as alternative but not as enjoyable as outdoors.

Jump rope is also good cardio work out... More intense than running as far as my experience goes.