It's Sheriff McAllister.  Here's my case:

1) Red John has a deep connection to the rural areas outside of the city.  Yes, he has been active in the city areas but it's not his normal stomping ground - look at season one finale which introduced both a friend and a lover of RJ, both of which were in a rural area.   And RJ was friends with that killer's dad, so RJ has deep roots in that area or community. 

2)  Rosaland mentions that RJ smells of "pine and earth" which seems to be answered because Jane thinks he was building a cabin or something...but, I think that's how he smells all the time because of where he lives and the life he leads.  His friends are from small towns - and so is his past...which leads us to...

3)   The barn where it all started.  Visualize is always the thing people mention when discussing RJ's first murder, but I actually think where it happened is important too. Another connection to the rural areas.  

4) The first time he met Jane they "shook hands" in a unique way that played up the idea of Jane being a false psychic...it's the perfect intro for the eventual villain...and could be used as a wrap around later when they meet for real.  

5)  Episode 2 dealt with a couple who kidnap and sexually assault young girls, just like the other couple from season 4 (I think) finale.  Also, it's possible the couple from episode 2 was being encouraged by RJ, but of course they died so...who knows...

6)  He's the suspect fewer people look at...why?  Because not much is known about him.  He doesn't really make much of an impression whenever he's on screen...which is odd since the actor who plays him is quite talented....maybe he's supposed to be bland?

7)  Most of the other RJ suspects are this season in serious nail biting episodes...but not Sheriff McAllister....he's practically in a romantic comedy...

again, we don't take him that seriously...perhaps it's by design?

In summery -- Red John has connection or works in law enforcement, plus he has a lot of friends  in the suburban and rural areas.   Sheriff McAllister. 

Hey all you fans out there!

I honestly think that Red John is more than just one person. I find him a little too random at times and also his knowledge and success rate seems to be little too far fetched...even for a genius/ psychic. So I think that Thomas McAllister, Ray Haffner, and Brett Partridge are all Red John.

Furthermore, I suspect that Thomas, Ray and Brett worked for a Visualize complex at one point during their younger years and went through a horrific experience. In the end they escaped their horrific experience, but they also developed a insane lust for blood and that might be were Mr. Stiles becomes more involved with them; by teaching them a code of conduct to operate by and eventually the name Red John and it's signature under which, they all operate separately.

Cheers, and please share your opinions on this theory!

At this point in time, Sheriff McAllister looks to me to be the most plausible Red John suspect.

I see that Brett Patridge may still be considered a suspect even though he's apparently dead. Even if he weren't dead, who was the guy who ambushed Lisbon while Patridge was obviously in his death throes? So it couldn't be Patridge.

It obviously wasn't Bob Kirkland given the events of Red Listed although the jury is still out on his twin brother. Assuming that the real RJ is restricted to Jane's list, I shall cross out Kirkland's brother as a suspect for now.

I think Gale Bertram is a little old to be running around committing murder. He's also a little too tall. That and Patrick Jane seems to be able to run intellectual circles around Bertram. The real RJ seems to be at least Patrick Jane's intellectual equal. Bertram doesn't seem to possess the necessary intellect that RJ clearly has.

Brett Stiles, while very intelligent, is also a little too old to be RJ. I don't see Stiles doing much by way of
hands on manual labour either (RJ has rough hands).

Ray Haffner may seem to be the best living suspect to fit RJs physical description but Patrick Jane made him look foolish when he was heading Jane's team. The real RJ wouldn't be so sloppy and foolish. Also, RJ is a very narcissistic character. I don't think he would have allowed Jane to intellectually dance around him as Jane did to Haffner without retribution of some sort.

Reede Smith doesn't fit the RJ description (although he is clearly mixed up in something sinister nonetheless). Smith is a little too pudgy and (while cunning) doesn't appear to be that smart.

Sheriff McAllister on the other hand steems to have quite the intellect. Look how he cleverly debated Jane as to the details of the body found in Season 6 Episode 3. Xander Berkley's portrayal of the McAllister character initially lead me to believe that he wasn't that smart. That changed in Episode 3. Physically, he could pull off RJs appearance although Haffner would be a better description. He is very adept at hunting.
And of course, he's afraid of pigeons.

If Bruno Heller is in fact telling us the truth that RJ is exclusively one of these suspects then I would have to bet on the Sheriff.

McAllister is the only one of the 7 suspects that has fallen for a Patrick Jane trick (see first episode), but then manages to squirm out of it with a plausible excuse.

Two suspects are dead now and Reede Smith appears to be an underling.  He also seems quite out of shape and doesn't fit the profile of Red John, since Red John would need to be manipulative in a charming manner.  He also doesn't seem to be old enough given the info we've learned about Red John's time spent at the barn in his youth.

Gale Bertram seems like he might simply be out of the loop.  It's possible that the mystery surrounding Gale Bertram that has been played up was due to the DHS and FBI request to funnel information to Kirkland about Jane. 

Bret Stiles is too sloppy with his followers.  He thrives on power given to him by his followers, but in doing so he doesn't choose them wisely.  I think there might be a tie between Bret Stiles and Red John.  It's possible that McAllister learned how to manipulate people from Bret Stiles, but rather than using that gift publicly, he uses it more discretely and selectively.  Bret Stiles would also likely have been identified by a psychologist in the same area as his Visionary.  Since Sophia didn't recognize him this helps rule out Bret Stiles.  She also described his posture as very poised and that fits McAllister more than Smith or Bertram.  When McAllister speaks politely it seems as though he's hiding something constantly.

It's easier to fake a lie when it's not a completely lie than if it were a whole lie.  I believe McAllister was actually afraid of birds, not heights.  We've seen Red John is likely left handed by how he holds the blade used to kill Patridge and McAllister saves Patrick from falling with his left hand.  A natural instinct to grab something important is almost always done with the dominant hand.

The DHS agents that broke into Jane's office stole the information for Kirkland, but nothing proves one of them wasn't a Red John conspirator and that agent could have sent the information to Red John as well.  If Red John had the same pool of 200 or so people he could have used some deduction to come to the same conclusion as Patrick.

Okay, It can't be Bertram. This is because he didn't recognize Kirkland when he allowed him to work on the red john case.. 
It can't be Reede Smith because he didn't even react to 'tiger tiger'. And he seems too young.

This leaves Mccallistar and Haffner...
Both are good whistlers Both are around 44, But we know McCallistar is afraid of pigeons as we saw in episode 3 at the end. I believed Haffner is Red John but it seems too obvious..Calling Lisbon by her first name etc. Next episode were going to find out why Haffner is not Red John just by looking at the promo.

I think it's between Haffner and McAllister.

I'm going with the sheriff, at least there is some mystery about him which makes him much more intriguing than Haffner who doesn't seem to have much of a personality..

Which one would you rather see as Red John?    GREEN  -  Haffner
                                                                        RED      -  Sheriff

Ever since Bruno Heller mentioned a key clue in the final sequence of 6x01 (The Desert Rose), there have been many guesses as to what that clue might be. Some guesses have been the '666' on the wall, the pigeons and Partridge quoting 'Tiger Tiger'.

I don't believe that it is any of these. In my opinion, the key clue which Heller mentioned in this scene, the fact that Red John is holding the blade which he used on Partridge in his left hand. This shows that Red John is a left hander. At the time, this is relatively meaningless because it is very difficult to determine which hand all of the suspects use and if one of them is, indeed left handed.

However, at the end of 6x03 (Wedding In Red), Jane slips on the roof whilst being held hostage by the murderer and manages to cling on by his fingertips. Sheriff Thomas McAllister arrives just in time to save Jane, killing the suspect in the process. When McAllister comes to help Jane up onto the roof, he reaches down with his left hand.

This confirms that both Thomas McAllister and Red John are left handed. Given that only 10% of the population are left handed and there were only six people remaining on Jane's list at this point in time, statistically, there is only one left hander on the list. McAllister is left handed. McAllister is Red John

Also, Xander Berkeley (who plays McAllister) had eight years removed from his age for his role as McAllister. Berkeley is 58. However, McAllister is only 50. This reduces his age when the murders in the barn (The Red Barn- Season 5 Episode 13) occurred from 33 to 25. This makes it much more likely that he was the 'kid' who Talbot said drew the face on the barn.
Additionally, the actor who is suspected to play young Red John (Nick Nordella) is 25 years old and resembles a young McAllister. Why change McAllister's age to fit these criteria exactly? Because Thomas McAllister is Red John :)