I'd recommend Majesty of the Seas over any of the other ships. She's had a refresh and they've added a few new dining options and upgraded various portions of the ship. I'm personnally not a fan of Carnival at all, tend to find it to be of a lower quality than Royal. NCL is somewhere between the two. If I had to personnally rank these in order (just my opinon) I'd place Majesty and Monarch on the top, NCL second and Carnival last.
All three lines will have a healty "party" atmophere on the shorter cruises as folks going on these tend to want to "get-away" for a weekend of fun.
Royal will always attempt to tender to the private island; as in any cruise any time of the year; weather plays a factor as to the safety of them tendering to/from the island. This will be true for NCL.