I voted "no preference". I think it's nice for family members to look like their parents, but I also think that the variety is pretty cool too.
Maybe a compromise could be something similar to VF1's system, where you normally get kids from the range between the parents' heads but sometimes get a "rare kid" aka one from outside that range, but have the "rare kids" be a little less... rare. I don't know if that's even possible.