I have been to as many as 20 cruises but I only use Princess cruise, holand america and lately celebrity (infinity). My experience on these ships are as follows:
Princess(Biggest and smallest ships): The big ships have two ballroom dancing lounge where they play ballroom musics every night. They also have a disco lounge (gorgeous place) at the top end tail of the ship. They play mostly hustle musics and disco but sometimes they play latin musics. They also have a country lounge where they play country music. In other words, they have 4 dance floors to enjoy.
Princess small ships: They have two dance floors where they play ballroom musics. In addition, before every show on the show lounge, people can dance on the stage with the orchestra, about 30 minutes everytime.
Holland america: They have both disco and ballroom dance floors. Two or three dance floors.
Celebrity Infinity: They have three dance floors. Two for ballroom and swing and a third one mostly hustle, swing and disco. There was a ballroom dancing compition which I was not prepared because I did not know and I did not bring a partner with me. There were several ballroom dancing professionals who compete. I met one and we decided to join the competition. It was my first time to compete although, I have been dancing for 45 years. We were voted by the passengers as one of the finalists. The grand final was on the stage where the show is held everynight. believe it or not, my partner and I won the championship. It was very memorable. On the final, before we danced, we were interviewed like what they do on OSCAR NIGHT in Hollywood and the interview was flsahed on the screen where we were about to dance and all the pasengers were there sitting and waiting for us. After the performance, our dance was also viewed on the ship TV everyday and night. As a remembrance, I was given a CD of the performance, a trophy and $200 credit.