can you share with us your process that you arrived at these two choices ?(i.e. how many cruise lines did you look at...did the itineray dictate the ship or was it reversed, drive vs fly to the port of embarcation etc) it might help us give you critical input ?
IMHO bottom line, I would do the 7 day vs the 6 day because it's really not a full 7 or 6 day, (last day is really not a day. first day, is really not a full day)..a day is not going to make a big difference and if the cost is equal
both have great beach options