Despite my name, I believe it is Bret Stiles, and for many reasons. It seems sort of obvious, but I could be far off.
1. We haven't seen him at all(once?) this season(6) if he is RJ, he may be wanting to lay low for a while. Or Bruno H is pulling our legs!
2. Visualize! Up until now,6.4, it has lead us to believe that RJ is with a group, Or a group of people himself (he is mar, he is many idea) my idea was that visualize is the cover up or some other group that BS is also in charge of. The way to know if you're in the other group inside visualize, the phrase Tyger, Tyger. In 6.4 they prove that Tyger Tyger is the phrase they say to show who they are. At the end of the episode (SPOILERS) the guard says Tyger Tyger, showing that it is more than just the 7 suspects in the group. Bret Stiles is in charge of visualize, which is a cover up for the RJ group.
3. Evidence from tape. The tape for the therapist says he is shorter than 6 foot. Bret is, and he is older than 30. To have commuted the crimes he would have to be older or at least 30(look at clues for this website) also, I could just see him being a whistler ;).
4. IMPORTANT! In 6.4 they kill bob Mcallister this proves it can not (NOT!) be the great red dragon idea. Now 2 of te suspects are dead, and the theory states only one is "dead". This discredits it, and shows that not all the suspects work for RJ.
IMHO, Bret stiles is red John. He hasn't been seen for a bit, he's old enough, and he is smart enough. He can use visualize as a cover up, and he is the only 1 of te 5 I could see being RJ.