There is more than just one hair typing system and while many may favor one over all the others, all bring some very vital information to the table. I've listed a few that you should get to know and you can then figure out which best suits your hair's needs.
In his book, Andre Talks Hair!, Andre Walker divides hair into these categories: type 1- straight hair, type 2- wavy hair, type 3- curly hair and type 4- kinky hair. Each of these categories also have sub-categories that divide them into different segments depending on texture and curl pattern. This is probably the most popular hair typing system that most naturals gravitate to.
This is Naturallycurly.com's adaptation of the Andre Walker method and many are very familiar with this and find it quite helpful.
You can find out more about hair typing (and the rest of this article) on my other blog Natural Hair For Beginners.