Larger speakers are sometimes better done with plywood, for weight savings. Plywood is lighter and more durable, particularly in the presence of water. But the downside is that sometimes plywood layers have voids, and where there are voids, there is debris in the voids that buzzes. Better quality plywoods like baltic birch are more likely to be void free, and so less likely to develop buzzes.

But for a speaker like the two π that is fairly small and used indoors, I'd go with MDF and use your favorite high-quality veneer finish.

Believe it or not, balsa's technically classified as a hardwood.

Chris