Solo cruisers meet on board
The best cruise line for singles is any ship with a lot of other singles on board. The truth is, if you are single and looking to meet your soul mate, the "Love Boat" concept that you can board almost any cruise ship and meet the perfect stranger is not even close to reality. The fact of the matter is that cruising is largely a couples experience, and if you do not do your research there is a very good chance you will spend more money than you wanted to (single cruisers traveling alone must pay a "single's supplement" if they occupy alone a cabin normally sold to two people), and spend most of the cruise talking to yourself.
Now this is not entirely true on some of the biggest ships from Carnival, Royal Caribbean and NCL, especially on the shorter cruises. However, there are still better ways to go about cruising if you are single.
Here's an idea. Say you are single and have someone at home special in mind? Invite them on a cruise. I can't think of a more romantic way to spark a romance. But be careful, because if it wasn't meant to be then you could be in for a long week. So here is another idea...
Go to CruiseMates' area for single cruisers , and look at all of the agencies offering singles cruises! A "singles cruise" is a charter of dozens of cabins on a specific sail date on a regular cruise ship where the company puts like-minded, same sex people together in cabins (to spare them the singles supplement) and sponsors plenty of activities for all of these single people to get to know the other singles in the group, like cocktail parties, special tours, dinners, etc. How much you participate is up to you. You may be there for romance, or you might just be there to avoid the singles supplement. Either way, the plus side is that you are guaranteed that there will people on board also sailing solo who will likely be ready to share excursions with you, and tables at dinner. Cruising is more fun when you share it with someone else, even if you love living alone.
Now, if you choose to ignore this advice, here are some ships you might book on your own and still have a good time:
Windjammer Barefoot Cruises? The truth is we used to recommend this cruise line as catering to singles by having large cabins that sleep as many as six people with no single's supplement. -- OK, it was more like summer camp, some of those cabins do not even have "facilities." Sadly, the cruise line has gone out of business.
One small cruise line has jumped in to fill the void left by Windjammer;
Carnival Cruise Lines If there is any one cruise line that usually has a fair number of singles aboard, it is Carnival. But a fair number these days is usually under five precent of all passengers, and they are often with roommates. So, if you are traveling solo, you either make it a threesome of break up a pair of friends. Answer? Take a friend of your own. Royal Caribbean's large ships are a close second in this category.
One cruise line we do not mention enough is Grand Circle Cruises. This cruise line, which does NOT sell through travel agents but only sells direct to cruisers, was first created by the same lady who dreamed up AARP. The line generally specializes in river cruises in unsual destinations. But it is a favorite with solo cruisers of all ages because it features many single cabins, or organized sharing, and special prices for solo cruisers in regular stateroom.
Holland America and Princess Cruise Line both offer a roommate matching service. They will put singles together if each potential roommate agrees to such a set up (it isn't mandatory, ever). Unfortunately, the only criteria they use to match roommates is gender and smoking preference. While it can save you a great deal of money over paying the singles supplement (like paying for two passengers, including port taxes, etc.), it is a gamble because you never know who you might end up with.
Most of the time, however, Holland America does not attract young, party-hardy types. Most of their singles tend to be women of 50 or older. So, the chance of good match is not too bad.
Crystal and Silversea both of these cruise lines often have more women and men on board due to the simple demographics of women outliving their husbands. These lines cater to single women (mostly elderly widows) by putting "gentlemen hosts" on board to dance and interact with them. Even though they know they are paid to be there, somehow it doesn't spoil the fun for these ladies.
But the fact is that every luxury cruise line has special offers for singles at times, and many of them now have staterooms just for singles. Check with a good travel agent to find out what is available.