What is better - Folder or Subdomain?

It`s always a complicated talk when it comes to domains vs folders. It mostly depends on what you're using them for. But for domain checking I`d go for subdomain rather than folder, that's because your website might be used for testing po or pharma domains, you wouldn't want a lot of website folders like http://yoursite.com/black-ships*-in-small-chick or whatever