I'm not totally saying it's Partridge... I've read that lots of people hate zombie theories about Brett. I only want to focus on what we know about RJ.
We assume that, like Patrick says, Roy Tagliaferro and Red John are the same person. Ok, so Rosalind Harker made a description of Roy. We can trust or not, but Patrick seems to trust her, since he asks her if Timothy Carter is Roy.The description says that Roy Tagliaferro is just under 6 feet tall, short straight hair, not muscolar, but not even soft, strong hands. Like I said we can trust or not this description, cause Rosalind is blind and above all she is fond of Roy.Then we can suppose to have seen him in the eighth episode of the second season, when Rebecca died with the poison and she smiled as a dreamer when she sees that man. We can suppose he is Red John. He has short dark hair and a desordered walk.In 2x23 we hear his voice for the first time. He modified his voice, but it doesn't seem a deep voice. Maybe a nasal voice.We know that Red John is related with Visualize. He worked in the farm in 1988. The priest said that a Young guy made the smile in the farm. So we can assume that now Red John is 45 or max 50.We had another description by Sophie Miller. Red John is a phobic. He's middle aged, good health, no family but many friends, great speaker, good posture and excellent whistler.And above all, we know he shook hands with Patrick. So...Brett Partridge: I admit it... I think he could be perfect. He fits Rosalind description, with the voice... He's intelligent, even if he seems a fool, cause he talked about Dickens and other stuff... I think he could hide a hidden personality. He died in 6x01. I'm not going to talk about zombie theories xD, but would it really be strange if Partridge faked his Death with the help of Tiger Tiger or all his friends? I don't understand why many of you think it could be so strange. It could be plausible. I love Jack Plotnick as an actor and I would be ok if Partridge didn't die.
Gale Bertram: No similar voice, no short straight hair. I think he's too tall. He calls someone in the 6x06 to inform about Jane's plan. Smith argued with him about what Jane knows in 6x02. I think he would be one of the worse Red John (my opionion).
Reede Smith: I like very much Drew Powell, but I wouldn't like him as Red John. He's a little bit too fat, way too tall and also quite Young. And I don't like the fact that he appeared in season 5. I would like that Red John was there also in the first seasons.
Ray Haffner: Good points for him. He fits with the description. He has the phobia of spiders. Good looking enouth to charm people, above all girls. The voice doesn't really fits. I think he's a bit too weak. But I support Partridge XD, so also Haffner could hide another personality. Perfect age and member of Visualize. He doesn't have the tattoo, but we have to study better the meaning of the tattoo. Maybe Tiger Tiger have the tattoo and not Red John.
Bret Stiles: Talking about personality... he would be perfect. Not really fitting with the description and with the voice, but I would accept it, beacause of the great carisma of the character. But... he's way too too old. He could be the father or better the mentor of Red John.
Bob Kirkland: He also died in 6x04. But he was kinda perfect for the description and the voice. And Kevin Corrigan made a great great work to describe the crazyness of the character. But he was a "good guy". I don't exclude the twin Brother. Maybe the person who saved him was Stiles and not Red John. But... Michael didn't shake the hands with Patrick.
Thomas McAllister: Xander Berkeley is sooo cool ahahah. I love all the Actors. The voice is too deep, but phisically he could be ok (not with the colour of the hair). I would accept him as Red John, but I think he's only a Tiger Tiger.
So... I would accept everyone but Bertram and Smith ahahah. But they seem to be the remaining suspects :( .
A question... why Red John would have put the bomb in the house if he was there too? He could have died in the explosion. Ok the theatrical part, but it would have been too Dangerous even for Red John being in that house.