No question: Carnival. We traveled with my 80 yr old dad, 16 yr old daughter and us in our 50's. Every age group is represented on that line with a predominance of single 30's. The food is much improved in the last 2 yrs (we went last on Fascination in May, 2000). Lobster night is a feature, as is the one awesome carved ice midnight buffet. My brother and wife went on Inspiration this last May and loved the ship. We sailed on her two yrs ago. Choose the destination of choice and have a ball. Prices are very reasonable. There is something to do all the time, esp at night. Rooms are a good size. Check out www.cruisereviews.com

Don't even try to smuggle in booze, though. They will confiscate it. Got to buy theirs. Many other cruise lines take the same attitude.