I think if I was going to have children my preference would be 2.
I also was suprised by the number of "only children" who posted here. It does seem that most people that I come in contact with out in the World have brothers or sisters.
Just a vauge generalization theory but maybe "only children" had more opportunities to travel while young (easier for the parents to have enough money left over for traveling, and easier to take 1 child on a long trip than it would be with say 4 children, etc.) and therefore, more likely to get that "wanderlust" into their system.
Just a thought since you asked. I'm sure their are lots of exceptions, as we've already seen from this discussion.