This thread presents two challenges; choosing one favourite song and checking out the previous sixteen pages of posts are both pretty demanding. So I´m going to stick to the here and now.

Concerning the previous page only:-
grindy´s Crow Jane scores high for authenticity, but I think the Derek Trucks version is a lot more exciting.
Chula´s Parisienne Walkways has some fabulous guitar, but for me GM´s singing brings the whole thing down with a bump.
Dwill´s Me and the Devil is my favourite of the three; although it´s a cover version, it gave me a genuine tingle as of something sinister.

And my own fave blues song ? Today at any rate, it´s from Country Joe and the Fish. There´s some passionate guitar playing from Barry The Fish, but the real punch is delivered by CJ´s haunting, intimate lyrics about his troubled times as Janis Joplin´s lover. In fact it´s a rather remarkable kiss-and-tell song of a kind that show-biz people rarely do. (I rather wish that John Lennon had done something similar about Yoko´s shortcomings, instead of all that loving-couple stuff he made us listen to!) :-

Hendrix - Red House

JB Hutto - Hawk Squat

currently it's:

Devil Got My Woman - Skip James

For now: Janis Joplin - Summertime (although it is not a pure blues)
I love listening to it during summer (you guessed it) because it never appeals to me!

I haven't read through this entire thread but does any one else consider Tom Waits legitimate Blue and Jazz? I'm not much into Blues and Jazz, but I do love Tom Waits.

He's a little to eclectic to really be shoehorned that way, although some elements are certainly there. His earlier stuff was at times relatively straightforward jazz/blues, but by now I just wouldn't know how to accurately describe what he does.

This is a good place for me to start

It's a generic answer but right now it's without a doubt Smokestack Lightnin'.
So primal and slimy. Howlin' Wolf is a colossus.