Style is always subjective and comes down to personal choice. Some people may choose something very traditional that blends in perfectly with their home's style and neighborhood's feel, while others will want to make a bold statement with a fixture that stands out dramatically.
Narrow down your style
Choosing a style that matches or blends well with your home style will give a more cohesive look to your home. A more modern home might look odd with an old-fashioned stained-glass style fixture and a nautical themed light would seem out of place on a southwestern styled stucco house. If you are not sure what style your home is, take a walk around your neighborhood to see what you like (or don't) about similar homes.
Add your personal style
If you are the homeowner, you will be seeing and using this light fixture more than anyone else, so the style must be something you are at least comfortable with, and hopefully love. As you browse options, imagine how each of these fixtures would feel greeting you each day as you return home. Pick something that will give you a feeling you enjoy!
If resale value is a consideration for you, selecting a more timeless design is a safer choice. Look for an outdoor flush mounted fixture that would look appropriate on almost any house on your street.