This is really a personal thing. What may work best for one family might not work best for another. One family may be happy with one child, while yet another family may not be happy until their family is Duggar sized (see link below).
I can not tell you what works for another family. I can not speak to how large or small someone else's family should be. I can only tell you what my husband and I want for our family.
Within a week of meeting my future husband, we had already discussed how big a family we would like to have. We started trying for a child less than a year after we met. Our daughter was born before we'd been together for two years. Right now, our daughter is 13 months old and I'm 8 weeks pregnant.
After our daughter was born, my husband and I discussed an issue that would come up at my 6 week postpartum check up... birth control. We talked about how large we want our family to be. What we decided is that we do not want to deny any blessings God may want to send our way. We chose to forgo any type of birth control. We are letting God choose our family size.
We would love to have a huge family (not necessarily ala Duggar, but still bigger than average), but we will be absolutely happy with however many children God sees fit to send our way!
There are many people out there just like us. I understand that there are also many people out there who want to stop at one or two children. That is, of course, their right. I just wish that there were more people who want fewer children than we do would have more respect for our decisions. I'm not going to put another woman down because she wants no children or only one or two, I wish the reverse were also always true.
Either way, though? We will do what we feel is right for our family.