My friends who have kids say they would never be without them. Life has changed for the better, they have grown in ways they never imagined they would, there is more meaning in everything, and every sacrifice is worth it.
My friends without kids say they never think about having them, that life is fantastic, that their relationships are solid and happy, career is exactly what they want or better, that they have the money and freedom to really enjoy life in ways that many of the people around them cannot.
So everyone's happy!
I will say that of my child having friends, a lot of them have said at one time or another that they wouldn't do it again if they had the choice. They love their kids and wouldn't be without them, but they wouldn't choose the same path if they could. Maybe it was sleeplessness and stress speaking. One friend described it as "Lots of joy, not a lot of happiness".