Talk to enough grandparents and one thing becomes clear: Because she's closer to the mother of the children, the maternal grandmother generally has a slight advantage. Or, as Audrey Berson […] put it: "She's my daughter, so I have the edge." Even so, Berson's co-grandmother works in the same town as the grandkids, and she sometimes meets the bus after school. "It bothers me," Berson said. "I wish it were me."
Source: wiktionary