anecdata but my experience on dating services is Christians, on average, look happy. No idea why. I'm atheist and not interested in dating a Christian because I could not support their beliefs. But, it's uncanny how often the pattern fits. I'm pretty confident, given 100 dating site profile photos, I can, far better than chance, guess which ones are Christian.
Note: I'm not saying Christians are happier than other religions. I live in the USA so there are more Christians than most other religions. I'm also not saying they actually are happier. I'm only saying they appear happier, on average, in their profile photos than the rest of the profiles. I find it very curious.