Assuming Jim hasn't changed his mind, he's told us what the big choice was. It's at the end of Grave Peril when Harry goes to save Susan. Our Harry summons a bunch of vengeful ghosts to kill the vampires when he could have absorbed their power and lashed out. The other Harry does the later.

Yeah, I read his two first novels and they are... fine? He went to the Jim Butcher school of making his protagonist a bit of a butt monkey, but in the case of Grimshaw Griswald Grimsby, he went a bit overboard and made him just pathetic in too many regards. While I definitely will get the third book of the series, coming out this month, so far the character hasn't convinced me yet that he is a worthy main protagonist, where Jim made Harry a bit pathetic, but also a lot of interesting in one book and has kept improving the character ever since.

It isn't clear though how they finally did, or I don't remember it.  What I remember is that a bunch of Wardens together took him down, but I don't believe it said just how they took him down.  Actually I don't think they did, as I said a couple of posts ago, I think Evil Bob is actually Kemmler. 

My tin hat theory!

What if Bob has been Kemmler all along?  Bob is a spirit, can he be killed? Don't think so unless maybe Mab can do it.  Is that why Bob fears Mab? Or is it because Mab knows who and what he is? Anyway, so the Wardens "kill" Kemmler, but they don't really because he retreats in his spirit form, or Bob.  Bob is very useful so a Warden like Justin steals him for his own use.  Justin was a Warden, he wasn't always evil, but what if having "Bob" in his possession corrupted him? Turning Justin warlock?  "Bob" would know about star born, "Bob" would have plans for such children.. Monkey wrench into the plan, Harry Dresden. Harry kills Justin, takes the skull and names the spirit, "Bob."  Just naming the spirit begins to transform him, also Harry orders him to forget the evil stuff he knew before Justin died.   Thus it was until Harry needed information about Kemmler and ordered a reluctant Bob to call him up.  Evil Bob emerged and nearly killed Harry, after that Bob was so horrified he cut himself off from his evil "memories" for good.  Those memories became Evil Bob who we met in Ghost Story, or was it really Kemmler?

To be honest, Mab was quite hard in her first appearances. I mean, we have no reason to believe she is evil per se but she is not only ruthless but apparently a sadist. Later, that was not so much the case. So, even when I agree with you Mira that Harry was quite biased in his storytelling, there are some facts that justified his perception.

Starborn is the key, I think.  Since Harry is starborn and has power over Outsiders and Outsiders have no power over him, Harry can say his name, or in this case use his name without harm or fear of attack from using it.

A good point.  So, that would probably only be the British (sounding) prisoner that Thomas might talk to, but only if that prisoner wanted to speak to Thomas. 

What I find striking about that encounter, is the three-eye addict; who would have been a total newbie to the world of magic compared to a wizard, recognized the name of the Walker, as if it was written in bold letters on Harry.

I had been presuming a sort of pre-programmed simulacrum, a miniature "spirit of knowledge" along the lines of Bob (or Lash & Bonea (and likely the Archive)) that Margaret had constructed for Harry before her death; albeit a vastly-lesser one.
But for this thing to be tracking all sorts of extra info -- Thomas, and Thomas' girlfriend -- happening out in the world, it'd need to be considerably more robust, not just pre-programming.  Able to conduct reconnaissance, to learn, to adapt... not really "lesser," in fact quite robust.