Mrs. Frono's "Koa topped F-30" (or whatever it is called) sounds really, really, really great. And I am a big fan of the regular F-30s with spruce tops and mahogany b/s, those don't need any changes...but that Koa one is something special. it just sounded incredible, from what I recall.
Also Paul Laguadoc who builds *electric guitars for Trey Anastasio from Phish, has many pricelss crown jewels that he has built. in all likelyhood the best sounding/looking/most valuable one is a particular koa topped 'doc (Languadoc), the one with the Ocelot inlaid on the headstock (Ocelot is a Phish song as well), and this guitar is widely acknowledged as the "Ocel-doc" by fans, it is the nicest/best of them all.