I submitted this theory before but I made some updates lately...
For me the main question is: Has Heller known who RJ for the last 3 years or is he only trying now to find a "good" RJ that will not disappoint us too much?
In the second case there is not much we can guess and we can only wait. And hope that the RJ plot will be at least interesting if not consequent with all that happened until now...
In the first case, where the writer planned a smart plot and carefully planted hints around the whole five seasons, we can try to find who RJ is by analyzing this hints. I strongly hope that this is the case and Heller is not playing with the plot anymore!
In case Heller did everything correctly, I am pretty sure that he himself wrote the main RJ story line without leaving the job to other screenwriters. My theory is that we should filter the seven suspects against the episodes written by Heller.
Here is the list of Heller's related episodes (Bruno Heller wrote only 17 episodes):
"Pilot": introduced Brett Partridge
"Red Hair and Silver Tape": introduced Sheriff Thomas McAllister
"Red John's Friends"
"Carnelian, Inc."
"Red John's Footsteps"
"Redemption"
"Black Gold and Red Blood"
"Code Red"
"Red Sky in the Morning"
"Red Sky at Night": introduced Gale Bertram
"Red Moon"
"Strawberries and Cream"
"Scarlet Ribbons"
"Cheap Burgundy"
"The Crimson Hat"
"The Crimson Ticket": introduced Reede Smith.
"Red John's Rules"
Surprise surprise!
Bret Stiles, Ray Haffner, Bob Kirkland were introduced in episodes not written and not directed by Heller! I really think we can exclude them because of this fact and related lesser importance. Why would RJ be presented to the audience by a second level author? The filler episodes are normally the one left to other screenwriters.
Since I really do not believe he would let the important task to introduce to us RED JOHN to somebody else... I will reduce the original seven persons list to these four:
Brett Partridge
Sheriff Thomas McAllister
Gale Bertram
Reede Smith
Let's talk about Reed Smith: he was introduced just a few episodes ago... there is no way he waited all these seasons to show us Red John. Furthermore, 2 years ago, Heller told us that in season 3 we got a *glimpse* at Red John. Reed Smith can be officially removed since he joined the show later.
We now have these suspects, and I strongly believe Red John is one of them (not seven suspects anykore but THREE):
Brett Partridge
Sheriff Thomas McAllister
Gale Bertram
Since McAllister has been a very minor character, and in my opinion Patridge was RJ in the first season and then was abandoned because he was too obvious... I would say that Heller's Red John is GALE BETRAM.
This supports many other good theories about him, mostly related to the Season 3 finale. The O'Laughling case, the hotel trick, the rope, the encounter with Timothy Carter happening in the Mall after Betram leaves and so on.