Sub-domain vs Directory Folder : I’m so confused.

I’ve been trying to do research to see what works better in search engines, sub-domains or directory folders and I just get more confused. When most people discuss the differences they either explain it in great detail that it goes over my head, or they give no real answers. What I want to know, is that if a sub-domain has only 5 pages or so in the site, would it be more beneficial as a directory? http://zoo.site.com or http://www.site.com/zoo/ The reason I ask is because, lately, I’ve heard that the more pages in your site can help you get found in search engines. I’ve also heard that sub-domains don’t count towards you site size. So would putting all my mini sites into directory folders on my main site be better? Or are they just fine in sub-domains? Does a search engine care? Will one be found easier than the other?