It all depends on your personal situation. Some moms are back at work quickly so the infant may be in care very young and it may or may not be family. You hope that you can trust your family more than a stranger but we've all heard 'those' stories.
I did try to go back to work when my daughter was 4 months old, having a friend I knew since grade school care for her. It didnt work just because I wasnt ready to be away yet! I never did have a casual babysitter for either of my kids (nights out etc). When I did return to work/school she was 3 and I used licenced care centers - more accountability and insurance coverage.