My spruce top has a very mellow sound, and I've heard the same with mango. Koa and its acacia kin, I believe, are a lot brighter. Most ukuleles I've seen are made of mahogany, which is I guess the middleman.
Thanks, glad I found this site, lot of helpful tips and advice. I didn't see the mgm video at first but that actually was awesome as I got to hear different ukes than reading about it.