I have been living in DB for 10 years. The following is my personal opinion.
I personally would not live in Tung Chung after living in DB. Although DB has quite a few high rise building, but the density is no way near as much as Tung Chung. You have to come to see what is a "real" low density of living.
There are many types of property in DB. It all depends on your budget.
I must say cost of living in DB is NOT cheap. We do not have wet market so the whole household depends on 1 supermarket. Transportation is also another factor you have to take into consideration.
The ferry is 24 hours service so it is not a problem for emergency and we also have 24 hours service doctors within the community.
Anyway, you have to come to see for yourself and decide for yourself.