Well, there seems to be a deep reason why it's hard to make headway on the "religion and happiness" question. People who care abour one tend to be skeptical of the other; happiness researchers tend to be pretty secular-minded, and scholars of religion find other, more tradition-specific categories more useful (blessedness, enlightenment, etc.). My article, when I finish it, will be about that mutual indifference; the challenge is arguing that it is a significant phenomenon! In the meantime, here are 8 generalizations culled from the relatively few "happiness studies" which bother to consider religious variables at all:
Rodney Stark and Jared Maier (in "Faith and Happiness," Review of Religious Research 50/1 (2008): 120-25) find that only the first and last of these generalizations are conclusively established by these studies. In other case the evidence is inconclusive, tending if anything against the generalization. Least inconclusive is 6, but it turns out the "religious effect" for both Protestants and Catholics is weaker than that for Jews.