Princess is indeed an excellent cruise line. I have totally enjoyed the times I have sailed her. Princess is a step above most, and she caters to that clique of cruisers, who enjoy the best in a quite civilized way.
Royal Carribean, on the other hand, has stunning ships, great food, and creates an atmosphere that excites you when you sail her. No stuffyness here, just an all around enjoyable vacation, be it family or just a couple, as well as singles.