Well, you've got 3 very different ships picked out both in size and activities. But, since you have an 18 year old, I would choose the Navigator of the Seas because it has so much more to do for kids.
In addition, I think everyone should sail on a Voyager class ship at least once in their life. There is nothing to compare to them, it was the smoothest cruise I ever had. Hardly knew I was on a ship.