As per my knowledge is concern only 3 Hats matters most in SEO:

1. White Hat SEO

2. Grey Hat SEO

3. Black Hat SEO

1. White Hat SEO:

White Hat SEO means completely following the ethical methods to acquire good rankings in search engines for a website. If a website really providing good information to visitors then white hat SEO works very well

and gives the best results. Now you have question that “what are white hat SEO methods?” All the methods which aren’t trying to cheat or manipulate search engines or visitors are called white hat SEO methods. I hope only few sites like Wikipedia, Google etc... follows white hat SEO methods.

2. Grey Hat SEO:

Grey Hat SEO means following combination of ethical and unethical methods to get fine rankings in Search Engines for a website. Most of the SEOs use Grey Hat SEO Methods to attain rankings. Grey Hat SEO works fine most of the time and most of the professionals recommend it. Grey Hat SEO methods aren’t unethical, it includes little stuffing of keywords in the site and back links etc. Now a day’s these methods are quite common while promoting website. Most of Corporate websites, Personal Blogs etc … follows Grey Hat SEO Methods.

3. Black Hat SEO:

Black Hat SEO stands to follow completely unethical which are used to cheat, manipulate search engines as well as users. In the past years search engines aren’t able to recognize these methods and difficult to find out and filter the websites which use Black Hat SEO techniques. Search engines are became smarter now and able to find out and blocks websites which use black hat techniques. Search Engine Quality Professional are working hardly and updating regularly the SE algorithms to give the best results to the visitors.