(Sophie) Preliminary diagnostic session with Jay Roth.
"Mr. Roth came in complaining of a recent issue with severe acrophobia. Fear of heights. He's middle-aged, in good health, with no stated prior history of psychiatric issues". 
"Middle aged" rules out Stiles, McAllister and maybe even Bertram. In season 6 episode 2, Reede Smith barks at Bertram that it is his job to know how much Jane knows. If Bertram were Red John, Reede wouldn't dare speak to him like that. I'd like to believe Red John maintains his alpha male status within his pack at all times. But I personally haven't noticed such behaviour when any of the suspects meet. Personally, I think Walter Mashburn is a nice candidate for Red John. Perhaps it will also be revealed that the suspect list was in fact bogus, something intended to keep Red John thinking he's ahead.