Stefanie, Welcome to cruise-chat! Hopefully you will find the information shared on this board helpful. As for which ship would be a better fit, there are few variables that must be considered. First, based on age only, I would think Carnival would be your best bet as there will definitely be more passengers in their 20's on the Imagination than the other ships. Holland America definitely caters to an older crowd and you will probably not find many other 20 something singles on that sailing (if that is important to you). If you are looking for a more multi-cultural experience, you might consider Costa. Announcements are made in 5 languages and about 1/2 of the passengers are European. Food and activities ae geared towards European tastes, so it is not a typical "American" Caribbean cruise experience. I enjoyed my cruise on Costa, but I have traveled a ot and was looking for something a little bit different. Hope I have helped a bit.