I don't have a lot to add to what's already on here but I feel like Brett Partridge is the most likely - probably unlucky with women so acts out a hatred, we don't know much about his past, just generally a bit creepy. But I have another question. If Rosalind Harker has met, and of course talked to, Red John, can't they play her a tape of the 7 suspects speaking? He could get interrogation tapes from most of them, record Brett Partridge at the next crime scene, play one of Brett Stile's speeches etc. I'm assuming he spoke to her in his 'normal' voice as who would help out somebody who spoke in Red John's creepy voice!
