Well, by now my guess would be Red John is Smith, because (if they're not kidding us) he is more likely to have a tattoo... also I think he is a very good actor (seen in s06e04) and an unknown and unratable variable...
BUT on the other side I'd accuse BERTRAM , because in the previous seasons he sometimes made strange phone calls, which were pretty suspicious, and Bruno Heller never told us more about it. Altough Jane helps him with playing poker, it could be just some kind of cover.
My THIRD theory would be, that RJ is someone from Lisbon's team... but that would fuck with everybody's head... so I hope this one's nonsense.
Greetz, Fabian from Austria