http://i.imgur.com/agLWD6c.png
This website was a big clue to begin with!

Its Sheriff Mcallister. His disciple was Sherriff Hardy yes a sheriff, nice nod by Heller,the biggest clue was in S1 how did this elude me!

RJ = Mcallister. RJ has a thing for women. So does the sheriff, remember how he approached van pelt.

Without much doubt, I suspect Mcallister because of the following points:

1. He is around 6 feet tall. 
2. He has rough hands 
3. He is not muscular or soft
4. He has short straight hair.
5. He is very calm in the roughest of times. Look at the next episode, even Brett Stiles got scared when Jane pointed a gun at him but Sheriff looked unmoved.
6. In the room with Bertram and Smith, look closely after Jane leaves, how Sheriff is staring at Bertram. He is the only one in the room who sounds a bit shocked when Jane talks about Sophie Miller. Jane cannot spot he is faking it as he is a pathological liar.
7. He wears the same shoes as RJ.
8. He said he likes to hunt anything with a face. That makes sense.
9. In season 6 episode 3, at the end look at him shooting the suspect, bull's eye. RJ too had shot accurately in season 2 finale
10. He shot with his right hand in the season 6 episode 3, while he uses his left hand to pull up Jane and to use his walkie talkie. Well apart from him, RJ is the only one who can use both hands easily.
11. None of the other suspects have been shown to be smarter than PJ except Stiles. But if you watch the episode 3 of season 2, you can clearly say that Sheriff is a lot smarter. Even Jane was surprised when he climbed the ladder. He said "where did you come from?" Only RJ has been able to outwit Jane till now. Maybe Sheriff got to know when they visited Napa that they had come to investigate him. Thats why he kept a close watch on Jane.
12. His age according to the script will be around 50 by now. So the Kid at that farm would be around 21 years old. Fits it.
13. The kid portraying Sheriff looks very much like him. Its got to be him.

Red John will be either Bertram or the Sherrif. (If we can trust the list)

Rigsby will be killed by http://www.imdb.com/media/rm86617856/nm0631381 for his investigations into kirklands death.

Next episode I presume we will see Haffner killed off, a long with Stiles being ruled out. Although I would like to see RJ as Haffner, my gut feeling tells me it won't be him. 

Assuming McAllister is RJ...

How poetic would it be if Patrick picked up on the fear of pigeons/birds and made one appear (like a carny/magician) and it frightened RJ to stumble and fall to his death. Again ironic given the fear of heights red herring.

Revenge without one shot fired.

Ok, this is the first time i ever put a theory in this website, i want to make it clear that i dont have a SINGLE suspect that i can say "Ok, im sure he is Red John", Heller is doing a great job and at this point we are all lost someway hahahahah.. So here i go.

Michael Kirkland: Bob Kirkland's twin has intriged me since his existence was mentioned, first thing that i noticed was Kirkland's voice, he has the same tone(?) of voice that RJ has (at least on the phone), could be that Michael's voice? Kirkland said that he and his brother were raised by a drunk father, and that Kirkland was the strongest, after he left, Michael stay with his father until he passed away, after that Michael met someone who help him (Kirkland assume that this man whas RJ), now i think.. Does anyone here ever played the game HEAVY RAIN? Two brothers, raised by a drunk father, one brother dies, the other becomes a serial killer, its a similar story, now IF, just IF, the man Michael met was actually Brett Stiles, who helped him after Michael joined Visualize, we all know that Stiles knows who is Red John, Michael could have become a serial killer after he murdered those two and the farm, and Stiles still is in touch with him, ALSO, AND VERY IMPORTANT, Rosalind Harker said that RJ smells like PINE, well... The house where Bob Kirkland was torturing people was registred at Michael's name, and its in the middle of a PINE FOREST! That caught my attention. So, could Michael be Red John? Yes, i guess.. Not shure, looking foward do know.

Raymond Haffner: Everthing is pointing him to be RJ, that makes me believe he is not, also, when everything pointed do Partridge, well, he died. Haffner match the fisical description, but, he does not have a personallity that i believe RJ would have (thats just my POV);

McAllister: Heller does said that since the first episode he already decided who was RJ, McAllister appeared on 1x02, he, someway, matches the fisical description, wear a wedding ring (we can see a ring on RJ's hand when he is holding a cup of tea), he is a great marksman, he has a great sense of smell, and is afraid of birds (or just dont like them), but as Patrick said something spooked RJ in the house at 6x01, pidgeons, maybe? 

Let me know what you think in the comments. Sorry if i type anything wrong, English is not my native language.