In my experience, I was playing on a Rousseau Jazz Metal which is BRIGHT (it gets to the point of sounding sharp, really). I picked up a JDX8 for 50 bucks (surprisingly cheap) and it was dark, but harder to pull out the bottom end. This coulda been the facing, really, but I would say if you want something darker, look for the JDX. I've never played it on an alto, but it was RICH on a tenor. It gave me a Dexter Gordon-esque sound. Pretty badass, if I dont say myself.
Im a little biased, so take this with a grain of salt. I've only ever played on Rousseau, Otto Link (which I thought was trash), and some nameless junk. But so far, the JDX has proven to be a beast, and it's cheap (which is all the more reason to buy the sucker).