Black hat SEO is a much faster way to get results as much as it is a faster way to get your site deleted from Google’s server. Black hat SEO techniques are all about manipulation and exploitation of Google’s algorithms.
Grey hat SEO is a little mix of the two approaches to SEO already mentioned above. As the name implies, it simply means being in that little grey area where it seems they’re doing what’s right and at the same time looking for Google’s trouble.