Answer:
Who will be using the site and the design theme selected for them.
Explanation:
The target user, will almost always define the way a website should be created as it should be optimised for your target audience. A search feature depends on the content of the site and weather it has lots of information or not. A horizontal or vertical menu also depends on the content, but it is not above the user, as it is meant to make it easier for them to navigate the site.
