He is my bet through elimination IF Red John is one man.

Brett Stiles - Red John was said to be a Visualise member as a young man at the farm - Brett is older than the other people who were talking about the young guy, also, he is the founder/leader of the org.

Reed, McAllister, Bertram and Kirkland - All have had meetings together and none seemed like a leader.

(Kirkland and Bertram's meeting was just the two of them, however, Kirkland did seem superior)

Haffner - Fits the description, was a Visualise member at the right time. - odd one out.

Second guess - Kirkland seems like the leader of the other 3, but may not be involved at all)

Third guess - McAllister seems very Red John cult leader-ish