"He is many"
Jane has narrowed the list to seven specifically because they were all people who could have been at each killing. If "he is many" then that means the main factor in narrowing the list is meaningless and it could be any of them or none of them.
I like Bertram for it.
The Kirkland possibly being the anti-Jane from his youth that was there for his good memory but grew up hating how easily things came to Jane is compelling but I think less likely.
Outside of the list, I think the Jane alter-ego is interesting (deep naps, blocked memories, insight into murders that could be explained by repressed memory couched as an observation).
Also, Rosalind Harker is interesting. Rosa=Red. She is not suspected because she is blind, but she could be faking or using her handicap as a cover. She is blind, not stupid, she seems oblivious to the fact she "dated" a murderer and that the morgue attendant was dead in her house as she played piano. Roy Tagliafero could be of her own making or even someone she killed and stole an identity.
Still I think Bertram for many of the reasons others have said (he said the poem when Jane wasn't around, he's a fisherman [Red John has disciples - a possible Jesus reference, i.e. fisher of men], he's intelligent, has resources, seemed to care less about getting rid of the team but always prioritizes keeping Jane within close watch, etc...)
