ok it has to be brett. in the episode that kirkland kills one of red john's men, he looks him dead in the eye before killing him "do you know who i am?" "no" so that says kirkland isnt red john. he knew who red john was and would not have had such a clueless look when he saw kirkland. kirkland is red john's right hand man most likely but not red john himself.

My money's on  Mr. Partridge.  In "Red John's Rules"  Partridge's assistant, Val Siskin, says, "I always wanted to work one of the famous killers" to which Partridge responds (under his breath): "Hi."  Now, I suppose Mr. Partridge, could be some other famous killer.....

Heres a little tid bit to consider.

In episode 8 Season 2, His Right Red Hand, we might actually see Red John as he passes Rebecca and poisons her. Her expression is telling that it is in fact him.
If you take this into consideration, there is a lot look at here that MIGHT shed some light. The weight, stature, walk, and the back of the individuals head is made apparent.
All these things could be cosmetically altered ore changed, sure, but maybe not.

Though the body type doesnt match Brett, everything else does no?
https://www.youtube.com/watch?v=1otRlA3PedI Heres the clip, though its super dark,. I studied this scene from the actual episode for quite awhile, hope that shed a bit of light~

I'm not sure this is a theory about RJ, but it just crossed my mind that if he was Forensic Investigator Brett Partridge, it would turn to be JUST LIKE IN DEXTER (a serial killer who's also a blood analyzer in the Forensic's Department). I don't think Bruno Heller would like to be called a ''copycat''.

http://insidetv.ew.com/2013/05/06/mentalist-finale-season-6-red-john-list/
I invite you all to check out this article of a convo with Bruno Heller. I guess he could be LYING to us, but I'd like to think he's not.

According to Heller:

Red John IS one of the seven people on the list.

Red John is NOT Jane.

Roselind Harker (the blind young woman who knows Roy Tagliaferro AKA Red John) has described him as being of average height (just under 6') with short, straight hair. He is neither strong nor weak in muscular build. He also has rough, calloused hands.

Combine that with a deleted scene in Season 1 (if that can be trusted) where Jane tells the others that RJ probably has brown hair and perhaps blue eyes and it narrows down the list by quite a bit.

Seems to me the only one's left are Robert Kirkland and Brett Partridge.
Both are around Jane's height of about 5' 11" (just under 6'). Both lean in build with short brown hair.
Kirkland is almost too obvious. They are really pushing his whole bad guy persona a little much this past season. Plus, in another earlier interview with Bruno Heller, he mentioned that RJ has been a sort of Where's Waldo in scenes all the way from the very first season. Kirkland is relatively new.

If Jane is to be believed, the only one with blue eyes and every other aspect would be Partridge from what I can see. He seems obsessed with the Red John cases. Killers love to put themselves right in the middle of their own investigations- being in forensics would certainly help that. He bugs Jane - another win for RJ there. Plus - he's just downright creepy.

Honestly, I'm kinda disappointed that Jane's father isn't on the list. I know, he's probably too old to be RJ and he hasn't been shown shaking Jane's hand in any episode ( if he even would), but THAT would make for interesting TV drama. Plus, he'd be more apt to know all of Jane's thoughts and actions.

But, in lieu of this new information. I'll have to go with Brett.

I think Red John is Brett Partridge for most of the reasons outlined already, i.e. he matches Rosalinds physical description, his voice, he and Patrick don't like each other, remember Lorelei said she was surprised they're not friends.  

I know Bruno Heller said there aren't any twists but I can't help but think Brett Stiles is involved somehow.  Maybe he's Partridges father?  (Both their first names are Brett, no one else on the show has the same name)  Maybe he's controlling him somehow, though a trance maybe, I know it sounds silly but Patrick is always putting people under a trance though.  And remember how Brett Stiles knew where Kristina Frye was, when no one else did.  And someone knew about Patricks childhood memories, in an early Visualize episode when Stiles told Jane where Frye was he made it sound like he knew everything, at least in comparison to Jane and RJ, which he dismissed as nothing compared to him. And she was in a catatonic state, maybe Brett Stiles made her like that?  But Brett Partridge does the killing?  

In any event I hope Brett Partridge is who the writers/produces/creator of the show go with.

Love to hear more input!

I believe Partridge is more likely to be Red John, mainly for 2 reasons:

1, He is not meant to be the obvious choice.  He has only appeared in very few episodes, but "key" ones-the pilot episode and 2 season finale ones. Episodes which are connected to Red John one way or the other. There must be a reason we only see him only there. I mean where is he in all the other crime scenes?

2. If you take season 2 finale and compare Partridge's voice in the beginning and Red Jonh's at the end of the episode, I believe you will find astounding similarities. Red John's voice is more clear and articulate, but tone and pitch are very alike