Bret Stiles.

He is very smart, an excellent manipulator, his followers see him as a
god, and is a member of Visualize (the leader). But, he doesn't fit very
well within Rosalind Harker's description of Roy Tagliaferro (it's
difficult to imagine him as her lover) nor with the few Red John
appearances on screen. He is almost bald, and Rosalind said that Roy has
straight hair. The man who killed Rebecca also has more hair.
Finally, the actor who plays him is 69 years old, what means he was 44
years old during the Ellinston barn murders in 1988. Too old to be
called "a kid". DISCARDED.

Gale Bertram.
 If he is Red John, it would explain the events of Strawberries and Cream:
how Red John noticed about Jane's trap, how he manipulated Jane to go
after the real Red John and later after O'Laughlin (conveniently leading
the conversation), and how Tim Carter
knew where he must to be. But, he also is bald, and if the man who
killed Rebecca was Bertram, escorts would have reacted to his presence.
And he is over 6 feet. DISCARDED.
 Raymond Haffner.
 He fits but is too obvious. Like I said about Kirkland in my previous
article, his role in the series is most likely as a red herring. It must
be noted also that @mentalistwriter said in september 15, 2011, that Red John has already appeared in previous episodes, but Ray's first appearance was two weeks later. However, he is almost certainly an accomplice of Red John. DISCARDED.

Reede Smith.
 I
will say it straight: he is fat. :-P I think if Red John was fat,
Rosalind would have mentioned it, but she limited herself to say that
Roy is "not muscular but not soft", what makes me think more about
someone thin, or at least thinner than Reede. In his appearances on
screen, Red John is clearly a thin man. And Reede's first appearance was
at Season 5. DISCARDED.
 Robert Kirkland.
Kirkland's role in the series is very clear: distract attention.
Producers want us to think he is a member of Red John's net or even Red
John himself. But this would be too simple and obvious, and The
Mentalist has taught us that the most obvious conclusions are never the
correct. My guess is that Kirkland is also hunting Red John and will end up being murdered by him  If Kirkland is Red John or a member of his net, what need could have
him to assault Jane's room and take pictures of his wall, if Red John
already knew the 7 suspects long before that happened? Red John knew about the 7 suspects before killing Lorelei, what happened in There Will Be Blood, but Kirkland assaulted Jane's room three episodes later, in Red Letter Day. Red
John had no need to reaffirm what he already knew. On the contrary, it
seems to confirm my assumption that Kirkland is hunting Red John.
DISCARDED.
Sheriff Thomas McAllister.
 He fits, and is almost a "John Doe". Despite he is a boring and too
random option, strictly I found no reason to discard him. I would need
to watch again the episode where he appears to see if I can find
something in particular. POSSIBLE.
 Brett Partridge.
 I
know most of you think that Brett is our guy. And I think so too. Of
the seven suspects, he is the one who has more probabilities, and the
only one who fits perfectly within the description of "Waldo" that
@mentalistwriter gave about Red John in the tweet I linked above (Ron
fit even better, but...). I also noticed something revealing during his
brief appearance in Red John's Rules:
when he is talking about Red John with his colleague, he said "I worked
Red John's murder scenes since he began", contradicting his own words
in Pilot when he implied that it was the first time he had seen a Red
John's smiley face. And, just when he says that (in Red John's
Rules), you can hear a sinister music playing in the background. Red John revealing himself? POSSIBLE.