There is no comparison there is far more on royal Caribbean for children of all ages.
My opinion will be slightly biased as I'm no great fan of NCL, but if teenagers are your concern it would have to be RCI everytime. Voyager & Freedom class ships have Rock climbing, Ice skating, Rollerbladeing & Surfboarding(only on Freedom Class) as well as the usual video arcades etc. Reading the reviews on this site should also help in your quest. Regards Wilba.