This is somewhat of a trick question:
Search engines look at how many pages down a given page is from the home page. And in this simplified case we are saying all incoming links go to the home page. In practice it is often that articles have links which give juice to the category and home pages because of naviation.
Search engines don't look at the URL to determine how many pages down a given page is from the home page. They look at the navigation structure.
example.com <- home page with external links to it.
example.com/category/ <- a category / menu / silo linked to by home page.
example.com/category/article1/ <- 2nd level down page linked to by category page.
example.com/article2/ <- Linked to by category page -- 2 clicks from home page.
example.com/category-article3/ <- linked to by category page -- 2 clicks from home page.
Noting navigation structure article1, article2, article3 are the same (navigation/structure wise). All are 2 clicks from the home page. Pushing everything to one directory off the home directory does not push these pages higher in search engines.
Note about page depth: The depth the robot will crawl is a moving
target: As of right now, Bing considers depth more important than
What URL structure is most common
The most common is example.com/category/article and the main menu pages, (categories), have more SEO juice than the article pages. But the structure is based on how the website owner organized content ... had he organized it differently the juice pattern would still match the navigation structure.
It is beneficial for the category / menu / silo page to have more link juice because that helps in pushing the article pages into search as they are created.
What if the URL is going to appear on paper
If a link is going to be printed on paper or otherwise used in wide circulation to new media? The shorter the URL the better.
A short URL is less likely to have a typo. But apart from the incoming links and citations short-url don't push up the page in search.