I don't even want to think about only doing weights or cardio. I feel a need to do both, plus occassional Yoga for stretching to avoid injury. But, then again, I'm the obsessive-compulsive type so don't listen to me. As long as you're doing some form of exercise you are ahead of most folks on this planet. And......Built is right, if you really only have time for one type of exercise lifting does more for you overall.