whta size is fit to a samll family?

We are wondering what size house we should buy. What is best tax benefit (property tax and mortage interest)to buy a house.

Small family (2 persons) moved to a new area, needs a house. We can buy a small house (1300-1800SF) with $130-150,000, mid-size (2000-2700SF) with $200,000-350,000, and up to a slight big house (3500-4000SF) with $400-500,000.

Too big, it seems unneccessary and waste, too small, it seems: not need to be so cheap.

Hard to make a decision.