I think for Mumbai or any place, Joint Family is better.
Now-a-days, most of the cases both parents (mother and father) are working to earn for good of the child's future. In such environment our elders and other family members are there to take care of of the children. Even if you keep maid servant, they will not care for your child as much as their grand-parents would do.
Another aspect is, care for Old-age elderly persons in the family. In this fast life we dont get time to go and visit our parents. When you are staying in same house, it is easier to look after their health and other needs.
Last but not the least : Children learn from their elders behavior. They will see us taking care of our parents and in-laws. One day they will also do the same things for us, when we would need company in our old-age.
Life is God's precious Gift...!!! Use it to the FULLEST.