Search Engines treats sub-domain as different site and subdirectory is an organizational component of an existing site. Generally, subdirectories are used when you need to describe what individual pages on a site are about, and sub-domains are used when you want to describe what an entire site is about.
Quick SEO Results: Based on my SEO practice, sub-directories gain faster keywords ranking as compared to sub-domains. The reason is that subdirectories are part of a existing domain which is already indexed and enjoying back links. If we are adding any new folder or page to the site then it will inherit the benefits of web site.
Easy Management: Technically, you need to put little more efforts for managing sub-domains as compared to sub-directories
Content Management: Sub-domains are definitely winner as compared to sub-directories for content management.