I'm going to see my friends dad's blues band play this weekend! I've never heard them before, so it should be new and exciting.

Guitar, but more specifically an acoustic one.

Neither? Because every instrument has such a different job that it's not really comparable? --I mean, it is to an extent, but not enough to decide the best--just your favorite... in which case would be the slide guitar. :D

peace out,
-nick

Nothing says blues to me like a wailing harmonica. Yeah the guitar is great, and a good raspy voice is nice, but I love that harmonica.

I'm not really into Blues, but I associate it with the saxophone for some reason.
Am I totally of the mark or is there some sense to it?

for blues i would say harmonica/guitar. for jazz, sax wins hands down for me :)

guitar and harmonica

piano can do well with it too.

I gotta second the vote on the slide guitar :)

Delta bluse style slide guitar...with some steel spoons as a rythm

Rubberband on a cigarbox ;-)