Are people happier when they're single, married, or partnered, but not married?

Married people do live longer.

I think some and some.. there's probably no one size fits all but as Slarti said studies to seem to indicate that those who are married live longer, have fewer health problems and are more content..  That's not to say it suits everyone and a very unhappy marriage would more than likely have the opposite effect.. But I think there are more marriage bashers out and about these days..people who are anti marriage or who have had a bad experience, or experiences... sure they have their own perspective but we mustn't forget that marriage can and does work for many people too.   Oh before I go.. I do recognise that one doesn't have to be married to be happy.. but a relationship or relationships which are nourishing and nurturing have to be a good thing 

It doesn't get any better than being happily married, particularly PK (PreKids). 

i think it depends more on the person, everyone is different

Yes. ;+

It depends on how many friends you have.

If it's a good marriage, then yes I'd say married people are happier.  Partnered up people are happier too, I think.

"Men are happy being single and women are happy changing men's minds."

People are happiest when they figure out how to make their own happiness, coupled or not.