Planning A Family

Paul and Teri Newlywed are planning a family. They've decided that they would like to have four children; no more no less. They really don't want all four boys or all four girls but would prefer to have more of a balanced brood. Once again, assuming a 50-50 chance for a boy or a girl, are they more likely to end up with... 

two boys and two girls or three of one sex and one of the other?