Clues are fun, and very pertinent in real life crime solving.  However, the only criteria needed in solving THIS mystery is the ability to correctly profile the mind of the show's creator, Bruno Heller. 

In as much, one needs to determine which of the VIABLE 'suspects' would make for the most exciting and watchable climax.  All of the remaining suspects, save one, would be vary ANTI-climactic as Red John.  The lone exception?  Malcolm McDowell as 'Bret Stiles'.  The ultimate bad guy in all his movies gets another crack to prove his lifetime achievement as 'Red John'.  None of the remaining candidates - all with careers as underlings in one way or another - would trump having McDowell say to Jane at the end, with bright evil eyes, "Won't you come with me Patrick?  It would be a GLORIOUS adventure!" (wry smile).

We're not cracking a real case, people.  We should be figuring out which 'suspect' would give the show the most bang for it's buck.  'Bret Stiles', the leader of the mysterious cult,  HAS TO be 'Red John'.