Joint family is best because, In joint family if there is any problem, it will be solved by senior member of the family. They will choose the correct way to follow their guidance. Nowadays, husband and wife go for profession to outside. They will not bother about their children because, children cared by the their parents (grandma/grandpa). Children have any health problem, they advised to take homely medicine.
In Single family, the decision will be taken by own. No experience of this problem they face more difficulties. They do not kept their children lonely. It will not safe. There is no guidance.