I think Ray Haffner makes the most sense. He has all the things going for him that Gale Bertram does (access to CBI, moving in a similar orbit to Jane, etc) plus he is a member of Visualize. Visualize is important because I think Stiles is actually a bigger problem than Red John.
I have a theory that Red John is a sub villain to Stiles. Stiles has a broader, national scope. He spoke like he had a friendly or paternal relationship to Red John back in season, what 2 or 3? Visualize indoctrination would give Red John the skills we know he has in manipulation, and frankly--cult building. Visualize could help him control his impulses. If this series continues past the killing or capture of Red John, I think Visualize will spit out another demon, or possibly several, until Stiles himself is neutralized.
So, I think Haffner is Red John. He has Visualize training, CBI training, and is a good looking, successful man building power and influence.
