I believe it's Ray Haffner for the following reasons:

1.) When he temporarily took over for Lisbon and was running the team pretty much everything he did or said revolved around Jane. He clearly wanted to work with Jane, observe him etc. He questioned Cho about Jane and if he thought he was smarter. For a man so high up in the CBI he acted foolishly falling for Jane's trick thus getting replaced with Lisbon who was put back in her old job. I believe this was his chance to work with Jane up close, really get to know him and his team and have a bit of a joke playing a "buffoon" they all underestimated (while having the last laugh). He didn't want the job long term and played along so he would get fired after learning what he needed to.

2.) Lorelei, who had never met Lisbon before, makes the statement "I think you're a little bit in love with her" to Patrick Jane. Why would she conclude this so quickly? I believe it's Red John's opinion she is repeating. It's also why Red John requested Teresa's head as proof of his loyalty. He knows how much Jane cares for her and was asking him to make the ultimate sacrifice to prove Jane was truly on his side knowing he probably wouldn't. Red John learned exactly how much. Jane cared for Lisbon when he worked so hard to get Lisbon her job back.

3.) When. Ray. Haffner appears again he tries to lure Lisbon away from the CBI with the offer of a lucrative job. When she declines he asks her if the real reason isn't that she loves her job but because of Jane. He says she "deserves better" and that Jane will eventually leave her. He makes no secret of the fact he thinks a lot of her and makes it as much about a choice between jane and him.

4.) In the Red Barn episode one of the first things he asks Lisbon about is how Jane pulled off the trick with the Red john symbol. He also doesn't answer lisbons question about working on the farm and asks if they are still friends.

5.) in one of the first episodes with Bret Stiles he implies he knows so much about Red John and that RJ wants to "take away" everyone that Jane cares about (like Ray is trying to do). He also says it's a kind of love RJ has for Jane. That's why RJ had kidnapped (Kristine?) the psychic. Ray and RJ have a similar fixation with. Lisbon in the last few seasons.

6.) Ray was involved with visualize and still is? Bret Stiles could be his father or former mentor which is why he knows so much and protects him.

7.) Red John "marked" Lisbon but didn't otherwise harm her. Does this mean he ran out of time or that he wants to "claim" her from Jane? He's never left anyone unharmed before.

8.) Ray has the most outwardly pleasant demeanor and is the best fit of the "descriptions" of Red. John. It's hard to imagine many of the other suspects being the romantic figure described by the women who have defended him, been brainwashed and killed for him.

9). He was in the CBI and would have had the knowledge to infiltrate the teams and turn Sam Bosco's secretary so she would murder him and Jane would get his case back.