I'm would guess that Red John isn't on the list, it would be too easy too little of a reveal.  My money is on Laroche for a couple of reasons, 

* If I was the director I would want to introduce the Red John casually on the show pretty early, around season 1
2-3 to make it a big reveal later on, LaRoche was introduced in season 3, so that fits

* You'd assume that the actor cast as Red John would have to be someone who could really pull off the gravitas of a serial killer mastermind. Only Laroche and possible Kirkland,Bret Stiles really comes to mind. But if I would cast the most wicked actor possible for the role it would sure be Pruitt Taylor Vince, those twitchy eyes are just down right creepy and he played the role very well before (in for instance Identity)

* It can't be someone on the team, that would just be stupid. I have a heard time seeing Van Pelt gave the time to run around working as a police *and* being a criminal mastermind

* Works for law enforcement so he has knowledge and insider information

* Ok this one is iffy, but Roche means "is celtic for uncertain origin" and French for "rock" it also seems to have something to do with red wine, I wouldn't be surprised if the name LaRoche is some clever play of words with Red John.

Runner up for me would have to be Bret Stiles, as a leader of Visualize he sure has the resources, has the age, the gravitas and one of the few who can give Jane's wit a run for his money.