There's a balance between to two and each effort has a demand on the body, both in a positive direction. Big gear, low cadence relies on muscle strength more than cardiovascular strength and will bring about growth to the involved muscles. High cadence "spinning" requires more cardiovascular strength, but is easier on the muscles and joints. Over time you'll naturally develop a balance between the two. Do you have more leg (Ullrich) or more lung (Armstrong)? Personally I value a stronger cardiovascular system. It's easy to have lots of muscle and a ****ty blood profile, not so with a strong cardiovascular system. In short, find your balance, ride lots, eat your veggies.