Ok, then lets start.

Brett Partridge----> DEAD (RJ associate)
Robert Kirkland----> DEAD actually hunting RJ on his own
Reede Smith----> ALIVE ACTIVE (RJ associate)
Sceriff Mcallister----> ALIVE ACTIVE (maybe RJ, phobia of birds)
Ray Haffner-----> ALIVE ACTIVE (maybe RJ, good whistler RJ, Visualize member, right age, was in the farm)
Bret Stiles----> ALIVE ACTIVE too old
Gale Bertram----> ALIVE ACTIVE too old, plus he is bald and RJ has hair

No I will discuss why in my opinion Ray Haffner is Red John and why the other are not.

Reede Smith is clearly an associate but not Red John himself. He is merely an associate.
Sceriff MCallister could be RJ because of his phobia (birds) which are shown to be at the house where Partridge got murdered, that's the reason MCallister couldn't kill Lisbon. (weak clue but keeps him in the game)
Gale Bertram is too old, plus he is bald and Rosalind Harker said that Red John has short straight hair. Not Bertram. Plus Bertram is an high rank CBI officer, is good to keep Red John informed about everything happens into the CBI and by this I mean everything regarding PJ and PJ cases. He is a member, of course he is. But he is not Red John.
Bret Stiles is too old to be Red John plus he, like Bertram is way too on sight. He has a public face. Can you imagine someone pupular going around and killing people? I think not. Bret Stiles created an organization (Visualize) that prepars people to become eventually Red John's disciples. He is an accomplice "I know more than you thing about you and Red John" said to Patrick in one episode. So he clearly is involved. But he is not Red John.
Ray Haffner is definetly the best option. Right age, he is muscular but not too much. He has got short straight hair like Rosalind said. He is smart and is a member of Visualize. He was in the farm in the same time Red John was and by not aswering Lisbon's when she asked if he was one of the boys at the farm... indirectly confirmed it. He worked for FBI, for CBI and now he is on his own. He placed his mens, he recruited them while he was in FBI (Smith, O'Glaughling) and in CBI (Bertram).
He is a good whistler. Rosalind said he had rough hands. He is shown lifting weights, why they show us that frame? He is Red John. 

Robert Kirland\Michael Kirkland I am amused reading others saying that Mike is Red John's right hand. Because is true and you all really smart figuring it out so quickly. Robert is sneaky but only because is on a hunt, and he knows is a deadly one. Michael being his twin is no different like him. When he asked "you know me" to the guy in the ospital was because if he aswered yes then I would have known that his brother was in the right direction but by saying yes he got assured that the RJ associate hadn't said anything. Michael is alive and active.