We have been on two other cruises both with Carnival.  We tried Royal Caribbean as friends had told us it was great for couples.  It was a nice ship and there weren't many kids so that is a plus for some people.  However, my husband and I like to play and it seemed the ship had more adult/senior couples.  We also like Carnival better with the ice cream and pizza 24 hours a day!  The ports of call were great.