If you are about to go on a cruise but you do not know which cruise line to chose then I have a few ideas that should help you to select the right cruise line. The major North American cruise lines, can quite easily be placed on a continuum from least expensive to most expensive and then in the opposite direction from most opulent and luxurious to least luxurious.
In addition, the most luxurious also tend to be the least fun. I will start with the fun side of cruises. Carnival calls itself "the funship" and for good reason. The guests are younger, the cruises tend to be more casual and relaxed. Carnival is also the least expensive of all the cruise lines.
Holland America, by contrast, is far more luxurious and more formal. It also tend to be one of the most expensive. I enjoyed my Holland America cruise because it was a place to dress more upscale at night and drink wine and really enjoy the finer things of life for a week.
Princess Cruises, was my personal favorite because we found that it was a fair compromise between the luxury and service of a Holland America cruise and the fun of a Carnival cruise. It was also priced, right in the middle.
You must bear in mind that even though a Carnival Ship and Norwegian Cruise Lines Ship are less formal than a Holland America and Celebrity, they are no less enjoyable cruises. I have been on many cruises and have never been disappointed.