From Arthur C. Brooks in the New York Times, "Scholars on both the left and right have studied this question extensively, and have reached a consensus that it is conservatives who possess the happiness edge. Many data sets show this. For example, the Pew Research Center in 2006 reported that conservative Republicans were 68 percent more likely than liberal Democrats to say they were “very happy” about their lives. This pattern has persisted for decades. The question isn’t whether this is true, but why.
"Many conservatives favor an explanation focusing on lifestyle differences, such as marriage and faith. They note that most conservatives are married; most liberals are not. (The percentages are 53 percent to 33 percent, according to my calculations using data from the 2004 General Social Survey, and almost none of the gap is due to the fact that liberals tend to be younger than conservatives.) Marriage and happiness go together. If two people are demographically the same but one is married and the other is not, the married person will be 18 percentage points more likely to say he or she is very happy than the unmarried person.
"The story on religion is much the same..."