It's not Gale Bertram - he is Kirklands mole in the inside organisation he approached Smith about, which explains the conspiratorial comment made between Kirkland and Bertram about Lisbon: "can we trust her?"

We also have no evidence it was Red John himself that had the tattoo - it could have been a Tyger Tyger member, and all the PI was trying to do was impart the sole bit of information she had in her dying moments.

We also know from things Heller has said that Red John is indeed on the list Jane made, which rules out other members of the team.

My suggestion is Stiles - he has already demonstrated enough personality to build an entire religion around himself, manipulate many people into doing his will, and shown that he has the ability to enter and exit the country at will (remember Red John beat Jane to Mexico to kill someone Jane was interested in talking to). He has powerful diplomatic friends, and a vast personal wealth to back his movements and actions.

His Visualize persona is just an act, something Red John is very good at doing when he wants or needs to as he is able to get close to a large range of people to carry out his wishes. He is manipulative and coercive, he is controlling and he loves his position of power.

If his claims of having cancer is also true, then that would also tie into Red John not wanting to play by any rules any more - he wants a sprint to the finish line with Jane before he can't do it any more.