I don't have empirical data to back this up, but I think people who are happily married are probably happier than single people. Nothing wrong with being single and I think there are plenty of single people who are happy and content. Just a general observation.
Good general observation!
Here is mine:
The best thing is to be happily married.
The second best thing is to be happily single.
The worst thing is to be unhappily married.
The second worst thing is to be unhappily single.