I'm surprised not to see more people looking at Alex Jane, Patrick's father. I think there's now an excellent case for considering him.

The show has been very careful to avoid giving definitive clues, and to include a lot of misdirection. Hence we should look for an answer that would provide an elegant conclusion, but that Heller has avoided hinting too directly.

Alex Jane is an obvious choice because of his absence. For someone so important in Patrick's development, he has received almost no coverage in the series, and that cannot be an accident. This absence from the plot is probably the strongest evidence pointing to him: he is being reserved for a future misdirection (which may have already started, in 'Red John's Rules'), or he is Red John himself. 

'Red John's Rules' confirmed that Red John's talents as a mentalist exceed Patrick's - guessing the seven names on his list, orchestrating the event so that Patrick would receive the disk that Lorelei recorded - all impressive feats. (It is, of course, possible that Sean Barlow's comments on John being a psychic are correct - but if you believe that, it takes you down a very different route.)  

It also shows that Red John has intimate knowledge of Patrick's childhood - not just the carnival circuit, but specifically of Patrick's upbringing. This includes information that almost certainly could not be obtained from third-parties - he selected the victim in that episode to make that point to Patrick. 

The seven people themselves are perhaps less compelling on purely dramatic grounds - none would give as satisfying a conclusion as it being Jane's father. A couple of them have solid grounds for suspicion, and Kirkland is at least an accomplice, but it's too obvious. Even the handshake clue may itself be a misdirection - after all, CBS and Heller have no obligation to tell the truth.