Swamp ash is a really good tone wood, and I'd probably pick it as my second favorite.
If I had to pick just one wood it would be cypress...a piece of really old cypress. I never would have known about this if it weren't for this great discovery:
My friend Pat at Resurrection Guitars worked for the county in which we live before making custom guitars full time. While doing that he had to pull a tree from the channel of the waterway at a local park. The tree turned out to be a large old cypress. By counting the rings they determined that it was 137 years old. Pat asked if he could have a piece of the old tree and was told he could have all of it if he liked. He took a large section home and after cutting away the worm eaten outer husk, he cut it up into planks and let it air dry. Because the tree had been sunmerged for so long it cured slowly and naturally with the oils leaching out over time. The planks dried with little or no checking and Pat made his first set neck, solid body electric guitar out of cypress. He'd never even thought about using cypress before this.
The guitar isn't much to look at as it's slab sided and painted in black nitro, but oh, what tone it has! The first thing you notice is how loud the guitar is. He's never been able to figure out why, but all the guitars made from planks from this tree are loud. Over the years Pat has made many guitars from other woods with the exact same body and neck shape. Not a single one of them has ever been as loud as those made from this tree. Weird sounding, I know, but absolutely the truth. The sound from this guitar is warm, clear, and very even accross the tonal spectrum. With a good tube amp it seems to respond to whatever tonal range you're trying to coax out of it. If you wan't clear, crisp highs, set the amp for it and the guitar delivers. Want mid heavy lead tones, set the amp up for them and the guitar delivers. It's almost like the guitar can sense what you wan't from it.
This guitar has garnered such a wide spread reputation that Pat gets regular requests to "borrow" it for for recording sessions. And not just from local muscians, from some pretty heavy hitters in the guitar world.
Now, if I can only find another 137 year old cypress tree that's been sitting underwater for a few decades. It's out there somewhere, just waiting...:thumbsup