I think Red John is Brett Stiles because:
-He is powerful because he is the leader of visualize
-The cult is brainwashed and afraid of him so he can get people to do what he wants.
-We know Red John drinks tea{1x23 & 4x13} and also Bret Stiles does{3x03}
-Bret Stiles shows interest in Jane and Red John
-He gave the location of Kristinna which led to nothing
-He is smart enought to be Red John as we have seen many times
-After Jane talks to Bret Stiles in 3x03 staright away we meet O'Lauglin who was a proven accomplice of Red John.I think that Bret Stiles sent O'Lauglin to spy on the investigation
-Bret Stiles has already killed and got away with it.
-In 3x03 we see Bret Stiles arrive in a limo which is Red Johns favourite choice of car
-Jane has even called him Red John