Is cardio or circuit training better?

Cardio and circuit training are both great forms of exercise. Circuit training has been shown to be just as beneficial as traditional forms of cardio training for improving, or contributing to improved fitness levels. Circuit training involves performing a series of resistance training exercises one after the other, with little to no rest between exercises. Cardio training is simply any kind of training that involves and places a stress on the cardiorespiratory system. Therefore, any kind of activity that increases your heart rate and breathing rate can be used as a form of cardio training. Some examples include: walking your dog, gardening, cycling, or weight training 

So which one is better? Since both are very beneficial forms of exercise, I'd have to say the better one is the one you enjoy doing the most.

Both are beneficial and are neither is better nor worse than the other - just different. Cardio training is any type of activity which elevates the heart rate. This can be walking at a fast pace, going up stairs, playing basketball, using a treadmill, or lifting weights at a fast tempo. Circuit training is method of weight training where one exercise is performed directly after another with minimal rest period; this type of training will also elevate the heart rate. A circuit training program can be a great way for an individual with limited time to simultaneously perform weight training and cardio to help with altering body composition. A typical circuit training program can include up to three sets of ten to fifteen repetitions.