The Guitar .

I'd say guitar -- with the ability to bend and slide, it is an extension of a voice
...and not just electric, I live blues played on an acoustic or a resonator.

A good, dirty harmonica sound is great for the blues, too, IMO.

Classic Blue,

Do me a favor. Go find the album "Hard Work" by John Handy. Listen to "Blues for MR. Jordan" After that, please let me know if you still think sax players sound bad playing the blues If you like that, I will add to the list of great blues sax players.

I will agree that there are a lot of Jazz/Blues cross overs that I think are sometimes out of the blues element. Those players you have to think out of the blues box and lean more to the Jazz side.

It's blues, of course the guitar is the most important! And if I had it my way, all blues guitars would be played be Stevie Ray Vaughan.

I would say 1 is the guitar 2 the harmonica

Chris

anything acoustic

bluesharp (harmonica)

Harmonica, but really I want to say bass, because blues just doesn't sound the same without the running bassline

There is no question in terms of history that the guitar is the most important instrument in Blues. The oldtime Bluesmen travelled a lot, played on street corners, hopped trains, and all that good stuff that has become legendary in the Blues. It's hard to walk the backstreets cryin' when you're carrying a piano.
Now, I'll take nothing away from piano's importance in the Blues, but it is not the root instrument in the genre.
The only other instrument that may compete is the Mississippi saxophone, but then there are rare moments when it is played without the company of guitar.