If you prefer informal cruising then look at Ocean Village in the Carribean. For more formal but still fab (though there is informal dining but MANY dress for the evening)try Sea Princess again in the Caribbean. I have been on both (for food though Sea Princess wins hands down)Look for ships around 70,000 tons if you want mid size. Large ships are all right but they dont have the atmosphere and take hours to get on and off at ports and embarkation/disembarkation. Have fun.
We are sailing on the Oriana this coming New Year and have been assured there is nothing like new years eve/day leaving madeira. Quite a few people have recommended this to us. Best of all the ships leaves from Southampton so no flying.