Is it more indicated for a geneticist desiring to map the X chromosome of the mother of a given family (the researcher does not have access to her DNA, only access to the genetic material of the offspring) to examine the chromosomes of her daughters or of her sons?

To examine the X DNA of a mother (suppose no access to her own material) it is more shown to study the genetic material of her sons as all X chromosomes of males come from the mother whereas the daughters have X chromosomes from the mother and from the father. By researching the material of the sons it is ensured that the studied X chromosome is from the mother.