Both.
Using folder style URLs is better for SEO however behind the scenes these are normally rewritten (using rewrite rules in .htaccess if using apache) to convert them to the appropriate get url.
So
http://domain.com/content/this-is-an-article
would get rewritten behind the scenes to
http://domain.com/content.php?title=this-is-an-article
To users of your website they see/use the folder version of the URL.
An example apache rewrite rule for this would be:
RewriteEngine on
RewriteRule ^content/([^/\.]+)/?$ content.php?title=$1 [L]