To be very honest all mass marketed lines are more alike than different. It is simply a matter of what you like to do. Yes, RCI is more active and probably, generaly has a little younger crowd. Princess probably would be judged with better food, but then, food is very subjective. We have had good and bad service on both, cabin sizes are similar and the entertainment is about the same.
Loyalist for either line will rave about what they like, but I think the best way is to judge for yourself. We usually pick our cruises by itinerary and price. We do have a favorite and it isn't either of these lines. As I said the mass marketed lines are quite similar.
ncl, carnival, HAL, Costa, RCI, commodore,chamdres,celebrity,Princess