Best blues vocalist

Let's hear it audiohounds. Air your opinions out to dry. To avoid tedious redundancy, state one of 3 categories (this way we don't have to wade through a comparison of Robert Johnson with Robert Plant!)

1. Pre-war blues
2. Electric blues
3. Blues-rock
There are too many for me to draw a full list, but here are a couple of women who might otherwise go unmentioned: Odetta and Koko Taylor. Check out "Gallows Pole" and "Wang Dang Doodle", respectively. I think pretty much everyone has taken a shot at "Wang Dang" and I'll take Koko's over the whole lot of 'em (including Howlin' Wolf's version). Just MHO.

The beauty of making such a list is in its impossibility. Forcing a choice gets your critical thinking cookin'. I have already changed my mind about what I wrote. It is inevitable.

NOTE: Maybe Tommy Jonson instead of Robert Wilkins?
A good answer to this silly question would be 1) Robert Johnson, 2) Otis Rush, 3) Etta James.