It depends on the musical task to which the instrument must be applied. Instruments are merely tools and one tool won't be ideal for every task. I prefer a Martin Dreadnought for bluegrass and sting band work because it can hold it's own with the other instruments and really cut through on the punch lines. Since I have a Dreadnought, I use it for folk music as well. For jazz I'd probably go for long for a big arch top similar to a 1939 Gibson Super 400.

Leon Redbone, in live performances, used to play a Harmony Soverign ($75 USD at the time). In his hands for the music he played, it was exactly the right tool. My second guitar is a hand built copy of a Fender Telecaster. It has a humbucker at the neck position and I keep it strung with heavy flat-wound strings. Good for Travis style, slide and screwing around wishing I could really play jazz.

The way I see it, we each ought to have a special room just to store all the guitars we need so every tune can be played with exactly the right "tool."

      - Mark