We have cruised several times on Carnavel NO regrets, we also have been on NCL NO regrets either, both were great !! I think it depends on the itinerary , length and time of year. We always go in Feb 7-12 days.....
Princess is noted for the older crowds (seniors) so we stay away from that line. Alaska isnt one I feel that the younger set goes on so I would say you would be safe on any line to stay away from the kids and younger 20's group....We sailed NCL in Hawaii and there wasnt any kids that I remember on that trip. We never go when there is any chance of schools breaks thats makes a huge difference on how may kids are sailing