You will have a great time on any of the major or premuim cruise lines. Remember, it is not so much the partying but rather the aesthetics of cruising. This means spending time watching the sunsets, or a walk out on deck at night and so on. All of the major cruise lines will feed you well and make sure that you have a comfortable cabin. This statement is based on the 12 cruises that my wife and I taken, and these cruises have been on all of the major and most of the premium cruise lines.
Factors for you to consider include price (how much can you afford and make sure that you get an all inclusive price), airplane arrangements (if any) cabin location, date of the cruise, ports of call, and your interests (cultural, historical, beaches, adventure such as hiking in rainforests, etc.)
There some very nice and reasonably priced 7 day cruises from San Diego and Los Angeles to the Mexican Riviera. And if you can wait until the month of May there are some excellent repositioning cruises to Alaska. There are also some excellent transatlantic cruises in April and early May.
Hope this helps.
Have a great time,