I use wind, water clarity, and depth to help me decide. When I want some flash, the wind is blowing, and the water is pretty shallow (2ft or less usually) Ill go with a spinnerbait. If its a little deeper and the water is more slick, then Ill pick up a crank. Also, I like spinnerbaits in water with at least 18 inches of visibilty, less then that Ill go with a crank most of the time. There isnt a clear cut answer to this. Just mess around and find out what works best on the lakes you fish.