Wow, there are many types of reiki, many I have found info about them on the net. I chose the two forms of reiki that I took. Usui Reiki is more on the physical plane. Karuna Reiki is more on the emotional plane as well as past lives and etc.
I took Karuna so that I would be able to help those with emotional problems and to heal their past lives if they were triggering the present. I have even worked on healing past lives with animals and had much success with it.
But each form does something different. I don't know them all because I only paid for the two versions of reiki that I needed, so if you want, do a search on reiki. That is how I found there are many forms spun off from what each person has been shown or enlightened to and taught. :)