We've cruised on 5 different cruise lines, and most of them have been on Carnival. We booked 2 Princess cruises at the same time; one for June 2012 and one for Jan 2013. This was our second Princess cruise and we had the same reactions both times: Princess just doesn't meet our needs the way Carnival does. We find the selection of food items in Princess' Horizon Court to be very limited, especially when compared to Carnival. Yes, Carnival's Lido Deck can feel hectic, but they have the best selection of food choices. On Princess the plan is to seat yourself in Horizon Court after you've gotten your food and then the staff will provide silverware and beverages. The problem is that getting beverages, both initially and especially refills, is sometimes a very slow & difficult process. On Carnival, you have to get your own silverware & drinks, but at least that's known up front and you don't have the frustration of trying to find a server to bring you these items. And in the end, there's simply a much greater selection of food items on Carnival's Lido Deck.
We found the food in Princess' MDR to be too exotic for our tastes. I ordered appetizers the first 3 nights but only liked it one time. On the remaining 7 nights there was nothing that was "normal" enough to entice me to try it. We have only had positive experiences in Carnival's MDR. Hubby likes to have a warm cup of hot chocolate before bedtime, and this has always been easy on Carnival since they have a hot choc dispenser right next to the coffee dispensers that are available 24/7. On Princess hubby asked for a hot choc at 11 PM in Horizon Court/Cafe Caribe. The server said it would cost $1.50. OK. She was gone a LONG time, and upon returning with the hot choc she said she had to go to a bar somewhere to get it. On subsequent nights the servers simply said they didn't have any hot choc--I guess they didn't want to trek to the bar.
The nighttime entertainment on Carnival is highly superior to Princess. Carnival has better productions and more of them. We enjoy Carnival's Comedy Club, and Princess has nothing similar. The layout of the showroom on Princess is not nearly as good as Carnival. On Carnival about half of the seats--all those on the lower level, closest to the stage--are "benches" that accommodate people of any size. On Princess 100% of the seats are "theater" seats that will not accommodate people of size. There were MANY people of size on our 2 Princess cruises, and I guess they either stood up or skipped the shows.
We couldn't help but notice that the passengers on Princess are older than what we see on Carnival. Princess, correctly so, caters to this group. We're not spring chickens but we've still got some spunk left in us. We find that we prefer to be among the younger passengers on Carnival, especially since we like Carnival's amenities better anyway. Carnival ships are just filled with energy and a sense of FUN that is lacking on Princess. We've never had an experience with an obnoxious passenger on Carnival (or any other line for that matter), so we'll just stick with what works better for us.
BTW, we selected these 2 Princess cruises based on itinerary and available dates. We were also interested in trying a line that has such a good reputation as a luxury line. We find that we can do with a little less sedate luxury and instead prefer a lively cruise line with the amenities that suit us.