I think number of children and their ages make a difference. My Mum is in her 70s, she's been a parent for half a century, much longer than she was alive prechildren so how should she compare? It's meaningless.
For me personally the baby years were horrible, no sleep, hormones all over the place, no help from family, career at a standstill and parenthood had a negative effect on DH and my relationship. Life before small children was happier, we were richer, more in love and better looking. But now our children are growing up and life is very good. But I don't think it's possible to compare before and after, never mind what it's like to compare now with a possible alternative life.
I also think it must be hard for those who are infertile reading all these self selecting comments about 'having a child completes me'. It is perfectly possible to have a happy and fufilling life without children and it's not good for a child to be so responsible for the happiness of their parents. Parenthood is one of many things you can do in life that gives you happiness or satisfaction.