Answer from Gail Akers: Both are beneficial and excellent approaches for improving your overall cardiovascular health. It is important to change up the intensity and duration of your cardiovascular program so you are less likely to plateau. Doing the same amount of duration and intensity each cardio session will not challenge your body enough, your body will have adapted to it and therefore not a lot of physiological changes are going to occur. Another thing to consider with these two approaches to cardovascular training will depend on your goals (such as weight loss, athletic performance, etc..) Be sure you are using diffrent types of amchines,( treadmill, eliptical, bike, etc..) in other words change it up such as one day use the treadmill and the next day the eliptical.

Answer from Jason Morgan: I agree with Gail, but I will add this...The most effective form of cardio is the one that you will do consistently. If you don't have the time to do longer duration cardio sessions, you are likely not to do them at all. The same holds true for the motivational factor of higher intensity sessions. You have to have the mental ability to push yourself to benefit from the shorter but much more intense sessions.