Cardio is necessary for any workout. I tell my clients to choose something that they have fun with, so if you like to bike or jog, pick the one that you have the most fun with, so you will be more likely to stick with it. Duration and intensity will determine the number of calories burned, but they are both great cardio choices. What it really comes down to is what you enjoy doing. Those of you who run or bike, which do you like better between the two and why does that work for you?