Penny has given some good information on Princess. I have been on both Princess and Celebrity and feel they are comparable in food, entertainment, and service. I only disagree with the size of the cabins. It can vary from ship to ship, but I think it can be very deceiving on room size. The same sized cabin can appear very different when laid out differently. If you compare the normal balcony on Princess in the BA-BG category to Carnival's normal balcony 8A-8G category the Carnival cabins are larger in square footage. When I say "normal" balcony, I mean a regular outside cabin with balcony. Not something called a mini-suite or suite. On most Carnival ships their balcony cabins are 185 Sq ft, and Princess balconies most ships range from 155-173. There are several Costa ships that are the same deck plan as Carnival ships such as the Costa Mediterranea, it's balcony cabin is also 185 sq ft. The Celebrity Millennium class ships 2a-2C balconies are 170 sq ft. So as you see there is a variety of cabin sizes. The amount of furniture in each cabin and the way it is arranged may make the cabin appear larger than it is.
I think it's great you want to try something different. If the price, itinerary, and ship, meets your needs on Princess then why not try it.