Harmoniicaaaaaaaaaaaaaaaaaaaaa.
Though I got to have me some guitar too.
You should listen to Groove Armada - Hands Of Time
and Tom Rothrock - Rollin' Crumblin'

harmonica is always great
and i've heard once or twice the sax
guitar and someother things as well

Tenor Sax gets my vote for best enhancer
 

Nice rich tones weaving through the tune. Ahhhhh. I think vocal would have to be the best instrument. That's where the emotion is that makes non musicians relate best too.

Harmonica or the blow-bottle.

Those 2 instruments always make me smile.

Harmonica is da best.

I also really like the saxophone..Alto and Tenor...the tenor has a richer sound to it but the alto plays an important role in a lot of jazz pieces...

harmonica - but guitar is the best too -

if you could blow into a guitar, THAT would be the best instrument

a fender stratocaster.

For those real low, down blues you've got to have the harmonica. It's how it all started.

easily the guitar
 

slide guitar on a straight tuning to D or G, cant beat that sound. ive got a few old hollow bodies and theres no better way to make that beaten up and original sound.