I think that unmarried people are happier long-term. Married people may be happy on their wedding
day, but every marriage has ups and downs.
At least fifty percent of marriages currently end in divorce. Single people are happier because they never
have to compromise. They are free to do
whatever they want, and that makes them happier.
Abusive relationships can be much more holding on a person if she has kids, is married, or both. Some people hold to saving their broken marriages even if there is no way it can be saved, or even worth saving. So some accept misery, confinement, entrapment, and a loveless marriage. People who don't marry and don't have children have less reason to stay in an emotionally damaging relationship thus can leave, and thus are happier (not always true I know).
For single people, well they may want to get married and settle, but many would also be happier as they are. Being single gives complete freedom. It means they can pretty much do anything they want without considering the needs of a partner.
For the record, I think it's fair to assume their are many happy married people too. It can bring emotional bonding, and completeness which is also good. There are many of happily married people in the world, but they aren't the happiest.
The happiest people in the world are children. Naive and impartial to the darker thoughts of the world, they see the world of bright sunshine and hope. The happiest children, are the ones who haven't yet been touched by natures twisted misfortunes, and are the people not yet bent and broken by the confides of time and existence.
Because of all these people, and children, I think unmarried people are the happiest people generally.
Again with the generalizations here. Some people are simply destined to be confirmed bachelors or bachelorettes, they like the single life and that's not going to change. Some people couldn't dream of anything other than being married and all that entails. Neither group can be happier or less happy than the other. It's all up to individual preference.
Unmarried people are happier. In my opinion, I think that sometimes this is true with anything in life. If you are not tied down to something, you still have your freedom and once that is taken away so is your happiness. However, some people were just not meant to get married and settle down. This is a choice and if you are happy with the one that you are with then you should not force each other to get marry. After all, it is just a piece of paper.
Marriage can help you become a better person because it's an exercise of humility, but that can make it difficult for many people to achieve happiness. Single people may prefer to improve themselves based on what friends and family will notice and tell them. Those who are married have a permanent companion that have much more impact on polishing them. Singles can be somewhat happier because their state of mind is more dependent on them alone, while those who are married depend on the other person to be happy.
There are some people out there who prefer being single or at least not married. Some people look at marriage is a complete burden, while others look at as a blessing. It really depends on the person and what makes them happy. Personally, I think marriage is the rout to happiness.
Happiness is not dictated by being married or by not being married. I believe there are people who are happy in either situation. Marriages can be wonderful, if the right people get married, at the right time. People who do not want to get married, should not. Being single or unattached will not signifigantly change your level of happiness.