There are 6 types of nen:
I'm not sure if all types occur equally, or if all types except specialist occur equally and specialist is less common, or if all of them occur at different rates.
I have attempted to research this question for an RPG I intend to run, however I have not found any information on this topic.
What is the distribution of nen type users? Information from any official source is welcome including all of the anime & manga.