Soprano ukes are a snap to build. Just build one with whatever wood, then do a show-and-tell for the rest of us. You'll be the automatic expert. To me there are only two varieties of hardwood, softer than EIR, and harder than EIR. Anything softer than EIR will probably make an OK top for instruments with a limited bass response (small ukes, dulcimers, etc.) Anything in the EIR range or harder will likely have limited response in range and volume. Just a quick way to line up the stranger varieties of wood we come across. I pretty much depend on the weight and thumbnail test to decide whether to make a top of a given wood. Instruments with a wide tonal response range probably need spruce tops. Guitars with mahogany or walnut tops look beautiful but usually sound too dry to me.