My wife and I are in our mid to late 30's - sailed on Princess and RCCL - 7 on Princess and 2 on RCCL. This was the first time taking our 3 kids on a cruise with us - we thought a 3-night would be a good introduction for them. We're glad we went and had a good time.
Our first cruises were all with Princess, and the two prior cruises to this one, we went on RCCL. Going back on a Princess cruise, we prefer RCCL. Princess is a good cruise line, but RCCL just suites our style better. Here's some of the comparisons: Princess does a great a great job of service in the buffet area, but we think RCCL has more selection to choose from. We like the option of coffee in the promenade on RCCL vs. having to go to the buffet for coffee on Princess. The shows we saw on Princess were quite good - Steve Moris and Motor City in the show lounge, and a juggler in the Atrium. We enjoy the game shows, Quest, and the Ice show on RCCL. And the promenade mall and dining room on the RCCL line (Freedom Class and Voyager Class) are so more grand than that on the Grand class of Princess. The fitness center on the Grand is much smaller than the one on RCCL and the view is blocked on Princess whereas the view on the RCCL Freedom Class and Voyager Class are much non-obstructed. Lastly, RCCL Freedom Class and Voyager Class have the rock climbing wall, miniature golf, and arcades that the Grand Princess didn't have. Other than those differences, the two cruise lines are very similar we think. After being on newer ships, you can tell that the Grand Princess is getting older.
Booking Staterooms: We booked 2 interior staterooms close to each other over the phone directly through Princess. They asked if we wanted "Complimentary Automatic Upgrades" and of course we said "yes" - who doesn't like to get upgraded. But beware of this, because they fail to mention that if you have more than one room booked and you want to be close to each other, they do not guarantee that you will be upgraded to rooms close to each other. We were automatically upgraded and notified after the fact via email, and one of our rooms was on deck 5 and the other on deck 14! I called to say we wanted our original rooms back because we could not be split up and they originally denied our request, saying they couldn't. We requested to talk to a manager and he also originally said they couldn't put us back, but after more talking, we were given our original state rooms back. We were on the line with Princess for over an hour to get our rooms back, so beware. We've also heard of others who get "upgraded" but end up in a room with the view of a life boat, or in a noisy area of the ship, so picking "auto upgrade" with Princess is risky business and I think they should stop doing that.
Good location - had a bit of a bad smell. My wife and daughter were in room D227 which didn't have a bad smell, but wouldn't recommend that one because you have to go through two doors to get into your room. Would not suggest choosing "Automatic Upgrades", especially if booking more than one stateroom in your party. An upgrade is not always better, and they don't guaranty multiple rooms to be upgraded next to each other.