Gadzooks, the choice, the choice. I hope to have five, a boy, a boy, girl, girl, and one last boy. If I believe I only have chance at one, we will have a PDG to help assure things come out right.
I see each experience having its own pros and cons.
Being in a family with siblings I can say the advantages was having someone to play multi-person games with. If something comes up broken, there are more suspects. There was someone there to share experiences with, on trips, what you discovered around town. You learn to negotiate, when it comes to toys and what games you play. You learn you have to be tolerant when it comes to space, privacy, access to things of the house. There is a built-in work force for getting chores done like the yard.
A cousin grew up as an only child. She didn’t have anyone she had to share or compete with in the family, but she also had to think of ways to stay entertained on her own; a bit hard to do before the Internet days. You rarely have to compete or negotiate TV access. You didn’t have to compete for deserts, etc. I have noticed many “only child” to be more mature in their talk and more patient around adults. As an only child you have the room to yourself, you can decorate it as you please, within your parent’s limitations.
Both has its good points and its bad points. I believe many families would be larger, but economics limits them to one or two.