Personally I love Carnival over Royal Carribean any day. My first cruise was Carnival and I loved all the different types of music and settings. The ship was colorful and lots of funt.
My second cruise was with Royal Carribean and it was a bit more "snobbish" I guess is the best word. In the dining room the matre'd removed the tails from my prawns at the table. I really could have done that. Anyways......
As for the ship, it was all wood / brass and it was Beautiful but I enjoyed the colorful ship better. Also there was only one place to dance where as on the Carnival there were about 3-4 to choose from
Anyways, hopes the above helps.
Have a great trip.