Hardness and weight are not measures of durability. A dense hard wood can be very brittle. Ash has excellent shock resistance, in spite of being a lighter wood. Ash is used in baseball bats and in many tools due to its resiliency, and was the wood of choice for the Vikings when making spears and axe handles. I have two pair of ash that I have gotten pretty beaten up, including from a lot of striking (not just drops). They have dings, but have not broken.
I have four pairs of white wax wood, and have broken them all on multiple occassions. Even so, they are all at least five years old and lasted a long time. I have also been able to glue them all back together, so all four are still in use. Mostly the breaks are at the top where the wood is thinner. I always wrap the tops of all my cord chucks in electrical tape now to protect them from drops.
I have a couple pairs of Brazillian Cherry that have held up well, although the ends are a bit chipped up from strking. They are a good mix of hardness and resiliency if you are looking for a heavier wood.
All the nunchaku that I have broken beyond repair are of unknown hardwood. Also, aside from Ash, white wax wood, and Brazillian Cherry, I don't know what my nunchaku are made of. I do have a pair of cocobolo, but they are my 2007 chuck off trophy chukcks, so I never use them, they are just for looking at
