Firstly, known facts:

- RJ is a white male. "Red Rover, Red Rover" (s04e23)

- RJ has shaken hands with Jane; they are known to each other, but are not friends. (s05e08)

- RJ's name possibly starts with "Ma". Note that there are three people who fit this criteria - namely, Madeleine Hightower, Lorelei Martins and Walter Mashburn. Out of these three, only Mashburn is plausible. (s01e11)

- RJ is "just under 6 feet tall; not muscular, but not soft either; short, straight hair; a gentle voice; rough, strong hands; he smelled of pine and nails and earth; and he liked to listen to me play the piano (especially Bach—he admired his rigour)." (s01e23)

- RJ has ties with Visualise. (s03e03)

- RJ has a fairly high pitched voice. (s02e23)

- It is still not clear what RJ meant when he recited 'The Tyger' (William Blake) to Jane. One might possibly deduce that it's an attempt to state that they are similar. Which is held up by recent episodes.

Mashburn - He's in a very good position to be a plausible suspect. He has the money, the power. He fits the descriptions to almost a tee. He is intellectual, narcissistic and above all competitive. It has been noted additionally that he has had several wives, the third -- he additionally states that "his third wife was in to all that goop" when talking about Jane's past as a psychic. No evidence thus far illustrates that RJ's third victim was a believer in the paranormal. From what we see, Mashburn's intellect does NOT level with that of Jane's.

Stiles - Again, in a very good position. It is stated that he was a friend of Ronald Reagan. He has illustrated both a strong knowledge of Jane and a connection with Red John. However, intellectually speaking, he has nothing on Jane. It is clear that Visualise is his first priority. However, it is acknowledged that Red John is adept at manipulating people, as is Bret Stiles.

J.J. LaRoche - It's a terrible shame that LaRoche isn't a plausible suspect, at all. His recitation of William Blake's 'Cradle Song' is such a tempting hint that he is at least an accomplice, of some sort, of Red John.

Luther Wainwright - Not only is he too small, he's too inexperienced. Also, he's dead.

CBI Ron - Seen walking alongside Kirkland on the way to Lisbon's office, and then seen to trail Kirkland as he leaves the CBI. Possibly a coincidence, but one might assume that he is, at least, an RJ informant. His name, of course, is a startling abbreviation of Red John, which, again, may or may not be a coincidence. No serious period of interaction occurs between Ron and Jane. This probably excludes him as a suspect.

Brett Partridge - A 'geek' by all accounts. It's clear that his understanding of Red John is limited. He does, however, suit most of the criteria. His position allows him infrequent, yet important interactions with Jane. His supposedly poor understanding of Red John COULD be a façade. Additionally, he illustrates the insecurities which Red John is shown to hold. His profile is suitable.

Out of the list provided, Mashburn is probably the strongest candidate. 

Partridge in my opinion is unlikely. Jane reads him like a book when they first meet, but yet struggles to figure out RJ. Jane instantly realises this man is physically turned on by murder which could be a plausible reason to be RJ. Lets not forget Red John has friends, a man of Partridges character is far from like-able or friendly. He is also too young.

Mashburn, well over 6ft tall. Has the power, fame and charm to sleep with a vast number of women so why sleep with Rosalind? I think the chances of him being Red John are really slim.

Brett Stiles. A man with mentalist power, connections in law enforcement, an intellect comparable to Red John and also not afraid to kill people/get them killed. BUT. Red John has a ritual, where as a murder Stiles is guilty for was nothing like Red Johns MO. Brett Stiles is also a very identifiable person, Rosalind would have mentioned Roy was very old, spoke very posh and is losing a considerable amount of hair.

Minelli. Joined the CBI soon after Red Johns mistake. Very like-able person, seems very soft and lovable. Loves to drink tea/coffee. He's the only other person in the whole of CBI other than Bosco and his team to know about the body with Red Johns mistake. He quits after the evidence against Red John is destroyed. After he quits, Red Johns personality changes almost as if he's quit too and he's looking for a new game to play. Only someone of really high power in the CBI could access the files and send that video to Van Pelt. He's the only person who knew what Tagliaferro meant. He went away on vacation supposedly to see his sick sister, shortly after that we find out Red John has built this hideout. His concern for Rosalind is clear and the way he holds that stuffed elephant is almost as if it means something to him. He's under 6ft tall, not weak but not muscular. Called Jane nuts when he said he had the upper hand on Red John.

Surely Virgil is RJ, No?

Virgil Minelli is an Italian name. Tagliaferro is also an Italian name.

Google : Dante and Virgil at the gates of hell.
Don't be too surprised when you see who the illustrator is.

Brett partridge is red john Because in s1.e01  &  s2.e23 he came in the crime scene why ???? because he want to see the murder’s he did’t do it and
why don’t he see crime scene that red john Committed its obvious he’s (rj)

sorry for my language