I’m going with Mashburn because he’s the only person who
fits the bill.



Think about it, Heller has described Red John as Moriarty.


Here’s a quote via Wikipedia:



“He is a man of good birth and
excellent education, endowed by nature with a phenomenal mathematical faculty.
At the age of twenty-one he wrote a treatise upon the binomial theorem which has had a European vogue. On the strength of
it, he won the mathematical chair at
one of our smaller universities, and had, to all appearances, a most brilliant
career before him. But the man had hereditary tendencies of the most diabolical
kind. A criminal strain ran in his blood, which, instead of being modified, was
increased and rendered infinitely more dangerous by his extraordinary mental
powers. Dark rumours gathered round him in the University town, and eventually
he was compelled to resign his chair and come down to London. He is the
Napoleon of crime, Watson. He is the organiser of half that is evil and of
nearly all that is undetected in this great city...”



—Holmes, "The Final Problem"

 



Add the whole good birth, excellent education, and extraordinary
mental powers with the ability to enthrall and seduce women.



Now take a list of the 7—the only person who remotely fits
the bill there is Stiles. I don’t think it’s him because he’s too old.  



Partridge: seems more like a geeky gore and slasher movie
fan boy, not Moriarty material.



Smith: not exactly a seducer of women, is he?



Bertram: too bland. Not remotely Moriarty material.



Haffner: is a follower and not a leader.



Kirkland: is dead, but if he wasn’t, then the same argument
applies. Not a brilliantly smart criminal mastermind.



McAllister: small town American sheriff. I don’t see him as
Moriarty.



I think the Tyger Tyger organization is more about
corruption in politics, law enforcement, and public service and not about
serial killers.



Visualize is about Stiles’ ego more than anything else,
though I would be interested in finding out if they use human blood for their
ceremonies (like the one in the last episode) and who provides it to them.



Now Mashburn fits the bill entirely—he’s rich, powerful,
suave when he wants to be, well read, and calculating. He’s smart enough to
have built a fortune. We also know that he went to reform schools when growing
up—perhaps he also did a stint in Visualize after (we know that many people who’ve
had problems turned to Visualize, so maybe Mashburn did the same).



Van Pelt: I always thought she was one of Red John’s
followers, but lately, I’m not too sure. I think it’d be too obvious if she
was.



Lisbon: I think she’s keeping something from Jane. I don’t
think she’s working for RJ or Tyger Tyger, but she is keeping something a
secret. 

Frye: could be Mashburn's ex wife's psychic perhaps? Or maybe even the ex wife herself?