o  Thomas McAllister - The character is simply creepy.  The fact that he isn't obvious would make it interesting.  (See below for why I ruled out the other 6.)

BTW, I was hoping S6 would be painted on a larger canvas.  Perhaps, RJ and friends could be one tentacle of an international terror/crime network.  That could explain the Homeland Security and FBI's interest in RJ.  Montero--Todd Johnson's friend (a known friend of RJ and serial cop killer)--was a gun-runner serving South/Central American terrorists and/or dictators.  RJ's slaughter of Bosco's team presumably disrupted the investigation of a major, international drug cartel.

Why I ruled out the other 6 RJ suspects:
o  Bob Kirkland - Several S5 shows provided lots of clues that Kirkland could be RJ.  Disappointingly obvious if Heller chose him.  He also comes across as weird and secretive more than evil.
o  Gale Bertram - Bertram was not nervous (per PJ) at the mall before PJ killed Timothy Carter (S3 finale).  Bertram had a plaque for bravery in his office, shown in one Strawberries and Cream episode (S3 finale).  Seems unlikely were he RJ.  He also has little hair--unlike the description of RJ's (blind) mistress, Rosalind Harker.
o  Brett Partridge - Too obvious.  Creepy, yes, but zero charisma. 
o  Ray Haffner - Could be, but he doesn't seem intelligent or evil enough.
o  Bret Stiles - He has the charisma, intelligence and organization.  But he is rather obvious.  He also seems too old.
o  Reede Smith - Could be, but he is too heavy to match Rosalind Harker's description.  So far, he has not been portrayed as intelligent or charismatic enough to be RJ.

. and Brett Partridge seem way too obvious.  The season 5 shows   They would be a let-down.  Bret Stiles seems too old.  Ray Haffner just didn't seem to have the charisma or intelligence.  And Reede Smith does not fit Rosalind Harker's physical description.

Two main suspects for me: Sheriff McAllister and Gale Bertram, in that specific order, with a lot of support from a bunch of characters we all know (Partridge, Styles, KFrye, CBI Ron, etc.) Not giving credit at all to Rosalind Harker's description of RJ since it's been demonstrated she might  be fooling us... What i take as a lead is Rebecca's reaction when she's approaching soon to poisoning her RJ at the prison and the body structure of that particular man, IMHO only similar to that of McAllister and/or Bertram... Many things have been detailed about Bertram but not enough have been said about the Sheriff so i'm leaning that might be a misleading omission for us to think RJ might be somebody else... We'll see in a few weeks... Enjoy S6!

A couple of thoughts.  First, I don't think RJ killed Jared Renfrew.  If you watch that scene carefully, the smiley face was painted on the right hand side of the bathroom, so it's not immediately visible when you walk in.  As you recall from the season 1 premiere, PJ knew that the killer was a RJ imposter because the smiley face was not the first thing you see when you walk into the room.  The killer is a RJ accomplice, possibly Bertram. 

Second, I'm pretty sure that the man who poisoned Rebecca is the real RJ.  The cops who escorted her did not recognize him, so I think we can rule out someone in CBI such as Bertram and Haffner.  Thomas McAllister makes sense in this regard since he's unknown outside of Napa Valley and is a sheriff, so he could have gained access into the building somehow. 

Third, I think Rosalind harker is still helping RJ.  I don't think PJ trusts her physical description of RJ since his very own list includes people who clearly don't fit the bill.

Of the seven people, the only people who were young enough to have been "the kid" at Elliston Barn, and still old enough to have been friends with Orvalle Tanner (Dumar/Sheriff Hardy's Dad) are : 

1. Sheriff Mcallister
2. Gale Bertram

Of these two, Sheriff Mcallister as Red John makes more sense. He and Tanner could've both been in Elliston Barn, and he's the one who could've most likely gotten Dumar a job in the Sheriff's office

The story of the couple of married assassins, Malcolm and Sandra Boatwright, in the McAllister's first episode, is similar at history of Timothy Carter, the Red John impersonator, and his wife Sally, in Strawberries and Cream/Scarlet Ribbons/Little Red Book. 
In Red John's Friends, Jared Renfrew
draw in the wall, before his death and with blood, the write: He is
Mar... That could be He is MacAllister, or not "He is Mar" but an
incomplete anagram as "l l c is mar...te", then "McAllister". Jared
could prepared this anagram when he was in prison; if Red John will kill
him, the killer would not have deleted the clue.

In Van Pelt file in Red Dawn (even if it is anachronistic, because it happened a few years after) there's the plot of part of McAllister episode, with the "redhead girls killer".

I have done the theory #4446 (blablabla). But I have to correct many mistakes.First , im not going to pay attention to the photo I have seen. So lets discover who is RJ.

List of the SEVEN SUSPECTS:

-Brett Patridge
-Bob Kirkland
-Thomas McAllister
-Reede Smith
-Gale Bertram
-Bret Stiles
-Raymond Haffner

Clue #1: Red John kills people that investigate him. The only one that can do this is Patrick Jane.
So , if we count that , Bob Kirkland can´t be.
Now , the list is like this:

-Brett Patridge
-Thomas McAllister
-Reede Smith
-Gale Bertram
-Bret Stiles
-Raymond Haffner

Clue #2 Lorelei told Patrick that Red John hadn´t became friends since they shaked hands.So , Bret Stiles  cant be , because he is Patricks´s friend.
Now the list is:
-Brett Patridge
-Thomas McAllister
-Reede Smith
-Gale Bertram
-Raymond Haffner

Clue #3: Roselind Harker told Patrick that Red John is less than 6 fit tall:

Brett Patridge: 5 ´11
Thomas McAllister: 6
Reede Smith: 6´3
Gale Bertram:6´3
Raymond Haffner: 6´1

Only leaving:

Brett Patridge
Thomas McAllister

Clue #4: Red John´s best friend was a Sheriff (1x23) isnt it a coincidence that Thomas McAllister , one of the suspects , is a Sheriff. We dont know if he worked on Vizualize , so perhaps it could be Raymond Haffner.

BUT KNOW ... SHERIFF THOMAS MCALLISTER IS RED JOHN (OR RAYMOND HAFFNER)

Just a thought.I know most of you believe that Sheriff Thomas McCallister isnt RJ and if he is it will be dissapointing.Anyway i dont know if he is RJ indeed but im pretty sure that he isnt just a Sheriff.If you pay attention in the conversation between him and Van Pelt at s01e02 especially when he says "I think you are drunk Mrs" you will see a man that tries to seduce Van Pelt(i dont know the reason and thats the key).I dont know if eventually McCallister will be RJ but the fact that he is on the list isnt random at all.