I want volume with clarity. I love good sustain too. The way I brace my tops is generally making me happy with that goal. I am finding that the back and side woods can then take that sound and make it more mellow or brash and every flavor in between.
I may be as far out in left field as it can be, but so far here are my conclusions about back and side woods. (this is subject to change as I build more instruments):
Hardwoods that have tight growth rings such as Maple and Oak generally give more bright sounds. Hardwoods that have wide or generally undefined growth rings (think rosewood or mahogany) generally give off more mellow, warmer tones.
Woods with both wide and narrow growth rings can give off the best of both worlds because they resonate at differing frequencies.
Like I said, its a theory and one I am trying to prove.