I seem to like koa wood on the back and sides and cedar on the top. Though one of my guitars is spruce and koa. I've had two guitars, over the years, with cedar and they seemed to sound great right out of the box (a fylde orsino and a taylor k14c). Mahogony is a wood I've also preferred over rosewood for the back and sides. I have, however played a couple other rosewood guitars that sounded great. I like a nice lower register, with good sustain (so the notes can ring against each other). So, I guess, whatever woods enhance that quality is what I will go for. I also have a custom made cittern (Irish bouzouki, mandolin on steroids) that was made with a spruce top and koa back and sides (with a middle birdseye maple piece), with a thicker body, that has a great sustain.