According to me the characters who fit better RJ's personality are
-Stiles: maybe too obvious
-Mashburn: but I'm not sure he fits RJ's physically description
_Bertram: He was my first suspect, why did he quote the same Blake's poem of RJ? it can't be a coincidence. Being so self-confident and making the challenge more interesting is typical of RJ.

Before I saw Red Sails in the sunset I had thought that Mr. Volker could have been a suspect too. He's rich, powerful, very self confident. But Lorelai let me think that PJ knew RJ's alias since pretty log time.
So kirkland wouldn't be a suspect too. Anyway I think Volker will come back soon, He's a too mysterious characters to leave him to gather dust.

About the other suspects, they don't convince me too much, surely some of them are involved (I'm sure GVP is already to RJ's side, I mean there's some dark in her) but they can't be RJ