as others have indicated this is a highly subjective question. It's like asking: "Which is the best car?" Now someone might suggest a Ferrari or Porsche, but if you need a car with a large trunk, those will probably be very bad choices for you.
An interesting question would e.g. be whether you would like to stick with a large ship. If you want to be truly pampered, there's no other way than taking a cruise on an upper-premium or luxury line - but those have smaller ships only. Celebrity and Holland America are great premium lines but - because of the number of passengers that most of their ships carry - simply cannot provide the same deluxe experience that Oceania Cruises (upper premium) or luxury lines such as Radisson Seven Seas, Crystal, Seabourn, Windstar or Silversea provide.
I have to agree with Cruise Fanatic that Carnival isn't half as bad as some people (who often haven't even taken a Carnival cruise) think. From my experience with them, they offer a cruise experience on par with that of Royal Caribbean International. While I prefer Royal Caribbean's more elegant (and less Las Vegas style) ships, I thought the food and service on Carnival was better. However, Carnival is certainly not an upscale cruise line (and neither is Royal Caribbean) so it doesn't fit your requirements. However, I would not hesitate to look into it for a family cruise.