The "tradition" with ukes is to use local wood. Koa just happens to be local in the Hawaiian Islands.
"African" mahogany comes in several flavors...Khaya being one and being considered in the trade as "a true mahogany", Sapele being another and not being considered a true mahogany; there are others as well. We've made Khaya ukes that sound just fine.
With our tenors, I am very deliberately going for a more "guitar-like" tone as well as feel. I'm trying to win guitar players over to uke; that's my central market target. As it is, a number of uke-centric players like the instruments, too, but I make no bones about the fact that I'm trying to appeal to guitar players with a big and warm sound. Our new concert ukes are much more traditional sounding, though not traditional looking. I prefer to let the Hawaiian builders have their thing, and we'll do ours here.
And that means I do like spruce for tops, and we usually use Adirondack.