Are all guests local or do you have to make travel arrangements? Then you may either avoid major holidays because of the higher travel costs or embrace them because people get vaction time. Beside also consider the weather depending on the type of wedding (Think "snowstorm" in commute to church or "melting cakes" in outdoor weddings)
Choosing a wedding date should be based around the couples desires for indoor/outdoor, scenery, anniversary, ect. Some others to keep in mind are Parents, siblings, grandparents, and wedding party.
Sometimes a wedding date can have a special meaning for the bride and the groom, but for the most part the date is chosen based on availablility of a specific venue, within a preferred season as many places book up a year in advance.
