Well, I gotta say, I'm REALLY happy that Reede Smith is not RJ. I actually started to like the character after the fact being revealed. Anyways:

I got 4 options: McAllister, Bertram, Partridge and Haffner.

First let's start with Partridge. I think he's dead. Of course it's possible for him to fake his death with the help of the Blake clan. Very unlikely but Partridge would be sure to not disappoint.

Next let's take Bertram down. At this point he's too obvious. There wouldn't be any twist if it was him. Sure he's a killer but not an RJ killer. But his the most recognizable character on the show after the CBI team so everybody would know who he is.

Now to Haffner. This guy is my second option just because he was my number 1 suspect. Part of Visualize, crush on Lisbon etc. all would make him a good Red John... But I think he was an innocent man killed in the bombing.

And now, sheriff Thomas McAllister. As the list was first shown everybody thought he was a bad option, me included. Until his second appearance. He was so friendly to Patrick, clearly wanted his friendship. Here's more reasons:
- He is played by Xander Berkeley, a talented actor who'd make a great performance.
- He could have faked the death easily, put the bomb in his hat and put a body in there with his blood or something then run away.
- 'He is Mar' He Is Mac Allister? He Is Marshal?
- Fits Rosalind's description the best out of all (except for Partridge and Kirkland who's dead)
- Appeared in the first season, the first episode to be titled with 'red'.
- He's like Waldo. Appearance in one episode and nobody suspects a thing even when put on the list.
- Has a fear of birds or just pidgeons. RJ has a fobia too of some sorts.
- Good shooter and so is Red John. They also wear same kind of boots (S2 finale).

I hope I'm right but I'll be satisfied with any of the four. Thanks for taking your time reading this!